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 $72.97   12.537%   $82.1182   $82.12   $82.10   $82.10  
  Purchase #2 $38.34   5.104%   $40.2969   $40.30   $40.30   $40.30  
  Purchase #3 $43.38   11.761%   $48.4819   $48.48   $48.50   $48.50  
  Purchase #4 $165.29   6.809%   $176.5446   $176.54   $176.55   $176.50  
  Purchase #5 $225.99   5.324%   $238.0217   $238.02   $238.00   $238.00  
  Purchase #6 $203.44   10.114%   $224.0159   $224.02   $224.00   $224.00  
  Purchase #7 $177.36   12.198%   $198.9944   $198.99   $199.00   $199.00  
  7 purchase totals = $926.77       $1,008.4736   $1,008.47   $1,008.45   $1,008.40