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 $201.98   5.803%   $213.7009   $213.70   $213.70   $213.70  
  Purchase #2 $46.48   11.380%   $51.7694   $51.77   $51.75   $51.80  
  Purchase #3 $165.32   10.394%   $182.5034   $182.50   $182.50   $182.50  
  Purchase #4 $26.86   6.316%   $28.5565   $28.56   $28.55   $28.60  
  Purchase #5 $209.67   12.401%   $235.6712   $235.67   $235.65   $235.70  
  Purchase #6 $200.53   7.649%   $215.8685   $215.87   $215.85   $215.90  
  Purchase #7 $136.75   9.662%   $149.9628   $149.96   $149.95   $150.00  
  7 purchase totals = $987.59       $1,078.0327   $1,078.03   $1,077.95   $1,078.20