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 $61.60   3.117%   $63.5201   $63.52   $63.50   $63.50  
  Purchase #2 $86.79   11.814%   $97.0434   $97.04   $97.05   $97.00  
  Purchase #3 $115.93   3.743%   $120.2693   $120.27   $120.25   $120.30  
  Purchase #4 $64.26   4.362%   $67.063   $67.06   $67.05   $67.10  
  Purchase #5 $173.31   10.257%   $191.0864   $191.09   $191.10   $191.10  
  Purchase #6 $225.51   7.290%   $241.9497   $241.95   $241.95   $241.90  
  Purchase #7 $31.98   5.477%   $33.7315   $33.73   $33.75   $33.70  
  7 purchase totals = $759.38       $814.6634   $814.66   $814.65   $814.60