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 $67.57   12.840%   $76.246   $76.25   $76.25   $76.20  
  Purchase #2 $62.35   3.342%   $64.4337   $64.43   $64.45   $64.40  
  Purchase #3 $57.77   11.113%   $64.19   $64.19   $64.20   $64.20  
  Purchase #4 $24.27   7.454%   $26.0791   $26.08   $26.10   $26.10  
  Purchase #5 $216.93   7.164%   $232.4709   $232.47   $232.45   $232.50  
  Purchase #6 $150.62   12.511%   $169.4641   $169.46   $169.45   $169.50  
  Purchase #7 $50.52   13.711%   $57.4468   $57.45   $57.45   $57.40  
  7 purchase totals = $630.03       $690.3306   $690.33   $690.35   $690.30