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 $43.38   4.173%   $45.1902   $45.19   $45.20   $45.20  
  Purchase #2 $189.52   8.719%   $206.0442   $206.04   $206.05   $206.00  
  Purchase #3 $225.99   8.199%   $244.5189   $244.52   $244.50   $244.50  
  Purchase #4 $82.32   11.785%   $92.0214   $92.02   $92.00   $92.00  
  Purchase #5 $72.56   5.646%   $76.6567   $76.66   $76.65   $76.70  
  Purchase #6 $169.93   5.665%   $179.5565   $179.56   $179.55   $179.60  
  Purchase #7 $60.28   6.722%   $64.332   $64.33   $64.35   $64.30  
  7 purchase totals = $843.98       $908.3199   $908.32   $908.30   $908.30