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 $55.91   10.421%   $61.7364   $61.74   $61.75   $61.70  
  Purchase #2 $47.68   5.474%   $50.29   $50.29   $50.30   $50.30  
  Purchase #3 $102.61   10.547%   $113.4323   $113.43   $113.45   $113.40  
  Purchase #4 $236.99   11.286%   $263.7367   $263.74   $263.75   $263.70  
  Purchase #5 $190.49   10.735%   $210.9391   $210.94   $210.95   $210.90  
  Purchase #6 $131.49   3.352%   $135.8975   $135.90   $135.90   $135.90  
  Purchase #7 $249.60   11.513%   $278.3364   $278.34   $278.35   $278.30  
  7 purchase totals = $1,014.77       $1,114.3684   $1,114.38   $1,114.45   $1,114.20