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 $66.35   11.582%   $74.0347   $74.03   $74.05   $74.00  
  Purchase #2 $234.52   9.253%   $256.2201   $256.22   $256.20   $256.20  
  Purchase #3 $8.36   10.744%   $9.2582   $9.26   $9.25   $9.30  
  Purchase #4 $187.61   11.399%   $208.9957   $209.00   $209.00   $209.00  
  Purchase #5 $70.59   8.145%   $76.3396   $76.34   $76.35   $76.30  
  Purchase #6 $158.50   10.271%   $174.7795   $174.78   $174.80   $174.80  
  Purchase #7 $135.43   7.499%   $145.5859   $145.59   $145.60   $145.60  
  7 purchase totals = $861.36       $945.2137   $945.22   $945.25   $945.20