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 $95.72   7.559%   $102.9555   $102.96   $102.95   $103.00  
  Purchase #2 $161.27   9.563%   $176.6923   $176.69   $176.70   $176.70  
  Purchase #3 $123.48   4.851%   $129.47   $129.47   $129.45   $129.50  
  Purchase #4 $37.97   12.300%   $42.6403   $42.64   $42.65   $42.60  
  Purchase #5 $170.78   11.297%   $190.073   $190.07   $190.05   $190.10  
  Purchase #6 $167.97   4.139%   $174.9223   $174.92   $174.90   $174.90  
  Purchase #7 $75.87   6.341%   $80.6809   $80.68   $80.70   $80.70  
  7 purchase totals = $833.06       $897.4343   $897.43   $897.40   $897.50