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 $217.98   8.463%   $236.4276   $236.43   $236.45   $236.40  
  Purchase #2 $110.48   5.275%   $116.3078   $116.31   $116.30   $116.30  
  Purchase #3 $48.32   7.372%   $51.8822   $51.88   $51.90   $51.90  
  Purchase #4 $247.44   8.248%   $267.8489   $267.85   $267.85   $267.80  
  Purchase #5 $140.74   3.177%   $145.2113   $145.21   $145.20   $145.20  
  Purchase #6 $175.85   5.769%   $185.9948   $185.99   $186.00   $186.00  
  Purchase #7 $57.51   12.764%   $64.8506   $64.85   $64.85   $64.90  
  7 purchase totals = $998.32       $1,068.5232   $1,068.52   $1,068.55   $1,068.50