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 $218.64   7.460%   $234.9505   $234.95   $234.95   $235.00  
  Purchase #2 $62.91   13.365%   $71.3179   $71.32   $71.30   $71.30  
  Purchase #3 $84.73   9.321%   $92.6277   $92.63   $92.65   $92.60  
  Purchase #4 $220.62   8.453%   $239.269   $239.27   $239.25   $239.30  
  Purchase #5 $236.57   12.636%   $266.463   $266.46   $266.45   $266.50  
  Purchase #6 $11.86   4.229%   $12.3616   $12.36   $12.35   $12.40  
  Purchase #7 $23.58   8.571%   $25.601   $25.60   $25.60   $25.60  
  7 purchase totals = $858.91       $942.5907   $942.59   $942.55   $942.70