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 $189.94   7.393%   $203.9823   $203.98   $204.00   $204.00  
  Purchase #2 $43.43   6.610%   $46.3007   $46.30   $46.30   $46.30  
  Purchase #3 $143.94   6.437%   $153.2054   $153.21   $153.20   $153.20  
  Purchase #4 $67.97   13.599%   $77.2132   $77.21   $77.20   $77.20  
  Purchase #5 $41.55   5.692%   $43.915   $43.92   $43.90   $43.90  
  Purchase #6 $206.70   5.464%   $217.9941   $217.99   $218.00   $218.00  
  Purchase #7 $91.78   7.609%   $98.7635   $98.76   $98.75   $98.80  
  7 purchase totals = $785.31       $841.3742   $841.37   $841.35   $841.40