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 $81.70   12.551%   $91.9542   $91.95   $91.95   $92.00  
  Purchase #2 $82.88   10.336%   $91.4465   $91.45   $91.45   $91.40  
  Purchase #3 $186.68   13.666%   $212.1917   $212.19   $212.20   $212.20  
  Purchase #4 $189.51   10.267%   $208.967   $208.97   $208.95   $209.00  
  Purchase #5 $58.61   6.231%   $62.262   $62.26   $62.25   $62.30  
  Purchase #6 $13.65   9.797%   $14.9873   $14.99   $15.00   $15.00  
  Purchase #7 $165.51   8.497%   $179.5734   $179.57   $179.55   $179.60  
  7 purchase totals = $778.54       $861.3821   $861.38   $861.35   $861.50