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 $42.57   10.702%   $47.1258   $47.13   $47.15   $47.10  
  Purchase #2 $250.61   3.381%   $259.0831   $259.08   $259.10   $259.10  
  Purchase #3 $60.67   8.159%   $65.6201   $65.62   $65.60   $65.60  
  Purchase #4 $216.87   4.392%   $226.3949   $226.39   $226.40   $226.40  
  Purchase #5 $193.50   4.219%   $201.6638   $201.66   $201.65   $201.70  
  Purchase #6 $83.62   10.847%   $92.6903   $92.69   $92.70   $92.70  
  Purchase #7 $177.54   3.863%   $184.3984   $184.40   $184.40   $184.40  
  7 purchase totals = $1,025.38       $1,076.9764   $1,076.97   $1,077.00   $1,077.00