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 $184.87   6.626%   $197.1195   $197.12   $197.10   $197.10  
  Purchase #2 $23.78   13.526%   $26.9965   $27.00   $27.00   $27.00  
  Purchase #3 $122.66   9.261%   $134.0195   $134.02   $134.00   $134.00  
  Purchase #4 $91.82   13.213%   $103.9522   $103.95   $103.95   $104.00  
  Purchase #5 $239.50   10.632%   $264.9636   $264.96   $264.95   $265.00  
  Purchase #6 $63.74   6.739%   $68.0354   $68.04   $68.05   $68.00  
  Purchase #7 $73.52   4.175%   $76.5895   $76.59   $76.60   $76.60  
  7 purchase totals = $799.89       $871.6762   $871.68   $871.65   $871.70