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 $58.42   10.643%   $64.6376   $64.64   $64.65   $64.60  
  Purchase #2 $204.73   6.391%   $217.8143   $217.81   $217.80   $217.80  
  Purchase #3 $113.84   5.702%   $120.3312   $120.33   $120.35   $120.30  
  Purchase #4 $83.85   11.449%   $93.45   $93.45   $93.45   $93.50  
  Purchase #5 $73.36   11.683%   $81.9306   $81.93   $81.95   $81.90  
  Purchase #6 $174.62   11.644%   $194.9528   $194.95   $194.95   $195.00  
  Purchase #7 $185.52   8.326%   $200.9664   $200.97   $200.95   $201.00  
  7 purchase totals = $894.34       $974.0829   $974.08   $974.10   $974.10