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 $197.47   8.165%   $213.5934   $213.59   $213.60   $213.60  
  Purchase #2 $235.45   6.609%   $251.0109   $251.01   $251.00   $251.00  
  Purchase #3 $71.74   7.442%   $77.0789   $77.08   $77.10   $77.10  
  Purchase #4 $211.97   8.125%   $229.1926   $229.19   $229.20   $229.20  
  Purchase #5 $92.49   13.482%   $104.9595   $104.96   $104.95   $105.00  
  Purchase #6 $5.36   12.324%   $6.0206   $6.02   $6.00   $6.00  
  Purchase #7 $84.97   12.365%   $95.4765   $95.48   $95.50   $95.50  
  7 purchase totals = $899.45       $977.3324   $977.33   $977.35   $977.40