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 $75.30   12.768%   $84.9143   $84.91   $84.90   $84.90  
  Purchase #2 $245.45   12.832%   $276.9461   $276.95   $276.95   $276.90  
  Purchase #3 $231.79   3.605%   $240.146   $240.15   $240.15   $240.10  
  Purchase #4 $229.74   3.790%   $238.4471   $238.45   $238.45   $238.40  
  Purchase #5 $66.63   10.244%   $73.4556   $73.46   $73.45   $73.50  
  Purchase #6 $88.92   6.819%   $94.9835   $94.98   $95.00   $95.00  
  Purchase #7 $94.30   11.837%   $105.4623   $105.46   $105.45   $105.50  
  7 purchase totals = $1,032.13       $1,114.3549   $1,114.36   $1,114.35   $1,114.30