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 $57.95   6.534%   $61.7365   $61.74   $61.75   $61.70  
  Purchase #2 $237.39   11.331%   $264.2887   $264.29   $264.30   $264.30  
  Purchase #3 $109.51   13.567%   $124.3672   $124.37   $124.35   $124.40  
  Purchase #4 $158.55   5.373%   $167.0689   $167.07   $167.05   $167.10  
  Purchase #5 $124.93   5.404%   $131.6812   $131.68   $131.70   $131.70  
  Purchase #6 $113.38   11.168%   $126.0423   $126.04   $126.05   $126.00  
  Purchase #7 $68.38   3.701%   $70.9107   $70.91   $70.90   $70.90  
  7 purchase totals = $870.09       $946.0955   $946.10   $946.10   $946.10