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 $58.98   8.256%   $63.8494   $63.85   $63.85   $63.80  
  Purchase #2 $227.94   13.463%   $258.6276   $258.63   $258.65   $258.60  
  Purchase #3 $39.82   9.538%   $43.618   $43.62   $43.60   $43.60  
  Purchase #4 $112.31   7.711%   $120.9702   $120.97   $120.95   $121.00  
  Purchase #5 $229.44   9.793%   $251.9091   $251.91   $251.90   $251.90  
  Purchase #6 $45.55   7.858%   $49.1293   $49.13   $49.15   $49.10  
  Purchase #7 $139.73   10.334%   $154.1697   $154.17   $154.15   $154.20  
  7 purchase totals = $853.77       $942.2733   $942.28   $942.25   $942.20