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 $238.48   10.688%   $263.9687   $263.97   $263.95   $264.00  
  Purchase #2 $144.25   4.129%   $150.2061   $150.21   $150.20   $150.20  
  Purchase #3 $58.71   8.469%   $63.6821   $63.68   $63.70   $63.70  
  Purchase #4 $84.90   7.165%   $90.9831   $90.98   $91.00   $91.00  
  Purchase #5 $177.54   11.323%   $197.6429   $197.64   $197.65   $197.60  
  Purchase #6 $205.74   3.374%   $212.6817   $212.68   $212.70   $212.70  
  Purchase #7 $39.75   5.874%   $42.0849   $42.08   $42.10   $42.10  
  7 purchase totals = $949.37       $1,021.2495   $1,021.24   $1,021.30   $1,021.30