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 $150.84   11.356%   $167.9694   $167.97   $167.95   $168.00  
  Purchase #2 $192.38   12.306%   $216.0543   $216.05   $216.05   $216.10  
  Purchase #3 $50.39   8.413%   $54.6293   $54.63   $54.65   $54.60  
  Purchase #4 $93.95   11.574%   $104.8238   $104.82   $104.80   $104.80  
  Purchase #5 $103.89   4.175%   $108.2274   $108.23   $108.25   $108.20  
  Purchase #6 $244.96   9.210%   $267.5208   $267.52   $267.50   $267.50  
  Purchase #7 $143.78   10.376%   $158.6986   $158.70   $158.70   $158.70  
  7 purchase totals = $980.19       $1,077.9236   $1,077.92   $1,077.90   $1,077.90