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 $214.36   12.678%   $241.5366   $241.54   $241.55   $241.50  
  Purchase #2 $245.79   7.701%   $264.7183   $264.72   $264.70   $264.70  
  Purchase #3 $151.56   12.125%   $169.9367   $169.94   $169.95   $169.90  
  Purchase #4 $64.67   9.361%   $70.7238   $70.72   $70.70   $70.70  
  Purchase #5 $129.96   5.663%   $137.3196   $137.32   $137.30   $137.30  
  Purchase #6 $52.89   12.179%   $59.3315   $59.33   $59.35   $59.30  
  Purchase #7 $30.94   11.147%   $34.3889   $34.39   $34.40   $34.40  
  7 purchase totals = $890.17       $977.9554   $977.96   $977.95   $977.80