Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $156.57   13.119%   $177.1104   $177.11   $177.10   $177.10  
  Purchase #2 $161.44   8.113%   $174.5376   $174.54   $174.55   $174.50  
  Purchase #3 $233.52   13.404%   $264.821   $264.82   $264.80   $264.80  
  Purchase #4 $176.32   11.536%   $196.6603   $196.66   $196.65   $196.70  
  Purchase #5 $204.43   5.794%   $216.2747   $216.27   $216.25   $216.30  
  Purchase #6 $163.76   5.642%   $172.9993   $173.00   $173.00   $173.00  
  Purchase #7 $194.49   3.684%   $201.655   $201.66   $201.65   $201.70  
  7 purchase totals = $1,290.53       $1,404.0583   $1,404.06   $1,404.00   $1,404.10