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 $200.58   13.835%   $228.3302   $228.33   $228.35   $228.30  
  Purchase #2 $250.85   6.323%   $266.7112   $266.71   $266.70   $266.70  
  Purchase #3 $58.75   6.352%   $62.4818   $62.48   $62.50   $62.50  
  Purchase #4 $159.80   6.303%   $169.8722   $169.87   $169.85   $169.90  
  Purchase #5 $40.99   5.686%   $43.3207   $43.32   $43.30   $43.30  
  Purchase #6 $58.49   11.611%   $65.2813   $65.28   $65.30   $65.30  
  Purchase #7 $7.72   7.800%   $8.3222   $8.32   $8.30   $8.30  
  7 purchase totals = $777.18       $844.3196   $844.31   $844.30   $844.30