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 $189.98   5.805%   $201.0083   $201.01   $201.00   $201.00  
  Purchase #2 $184.84   13.141%   $209.1298   $209.13   $209.15   $209.10  
  Purchase #3 $111.25   11.306%   $123.8279   $123.83   $123.85   $123.80  
  Purchase #4 $43.83   11.539%   $48.8875   $48.89   $48.90   $48.90  
  Purchase #5 $250.76   6.603%   $267.3177   $267.32   $267.30   $267.30  
  Purchase #6 $68.61   9.710%   $75.272   $75.27   $75.25   $75.30  
  Purchase #7 $24.50   8.701%   $26.6317   $26.63   $26.65   $26.60  
  7 purchase totals = $873.77       $952.0749   $952.08   $952.10   $952.00