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 $217.86   13.281%   $246.794   $246.79   $246.80   $246.80  
  Purchase #2 $69.58   10.514%   $76.8956   $76.90   $76.90   $76.90  
  Purchase #3 $126.33   9.586%   $138.44   $138.44   $138.45   $138.40  
  Purchase #4 $158.96   12.196%   $178.3468   $178.35   $178.35   $178.30  
  Purchase #5 $229.51   7.337%   $246.3491   $246.35   $246.35   $246.30  
  Purchase #6 $84.95   4.276%   $88.5825   $88.58   $88.60   $88.60  
  Purchase #7 $176.47   7.186%   $189.1511   $189.15   $189.15   $189.20  
  7 purchase totals = $1,063.66       $1,164.5591   $1,164.56   $1,164.60   $1,164.50