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 $55.32   12.184%   $62.0602   $62.06   $62.05   $62.10  
  Purchase #2 $25.39   6.312%   $26.9926   $26.99   $27.00   $27.00  
  Purchase #3 $78.51   8.150%   $84.9086   $84.91   $84.90   $84.90  
  Purchase #4 $211.85   10.258%   $233.5816   $233.58   $233.60   $233.60  
  Purchase #5 $159.48   9.351%   $174.393   $174.39   $174.40   $174.40  
  Purchase #6 $137.71   5.855%   $145.7729   $145.77   $145.75   $145.80  
  Purchase #7 $131.28   12.711%   $147.967   $147.97   $147.95   $148.00  
  7 purchase totals = $799.54       $875.6759   $875.67   $875.65   $875.80