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 $241.40   11.306%   $268.6927   $268.69   $268.70   $268.70  
  Purchase #2 $95.35   6.133%   $101.1978   $101.20   $101.20   $101.20  
  Purchase #3 $144.35   11.555%   $161.0296   $161.03   $161.05   $161.00  
  Purchase #4 $105.96   13.605%   $120.3759   $120.38   $120.40   $120.40  
  Purchase #5 $38.92   3.238%   $40.1802   $40.18   $40.20   $40.20  
  Purchase #6 $108.87   11.330%   $121.205   $121.21   $121.20   $121.20  
  Purchase #7 $136.65   3.713%   $141.7238   $141.72   $141.70   $141.70  
  7 purchase totals = $871.50       $954.4050   $954.41   $954.45   $954.40