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 $111.49   12.717%   $125.6682   $125.67   $125.65   $125.70  
  Purchase #2 $30.51   11.479%   $34.0122   $34.01   $34.00   $34.00  
  Purchase #3 $41.31   5.270%   $43.487   $43.49   $43.50   $43.50  
  Purchase #4 $53.60   9.673%   $58.7847   $58.78   $58.80   $58.80  
  Purchase #5 $169.82   3.407%   $175.6058   $175.61   $175.60   $175.60  
  Purchase #6 $60.87   6.766%   $64.9885   $64.99   $65.00   $65.00  
  Purchase #7 $194.31   4.555%   $203.1608   $203.16   $203.15   $203.20  
  7 purchase totals = $661.91       $705.7072   $705.71   $705.70   $705.80