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 $54.61   6.798%   $58.3224   $58.32   $58.30   $58.30  
  Purchase #2 $244.25   12.596%   $275.0157   $275.02   $275.00   $275.00  
  Purchase #3 $213.67   13.406%   $242.3146   $242.31   $242.30   $242.30  
  Purchase #4 $169.72   6.192%   $180.2291   $180.23   $180.25   $180.20  
  Purchase #5 $94.88   6.273%   $100.8318   $100.83   $100.85   $100.80  
  Purchase #6 $62.45   12.268%   $70.1114   $70.11   $70.10   $70.10  
  Purchase #7 $157.99   12.568%   $177.8462   $177.85   $177.85   $177.80  
  7 purchase totals = $997.57       $1,104.6712   $1,104.67   $1,104.65   $1,104.50