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 $246.29   11.536%   $274.702   $274.70   $274.70   $274.70  
  Purchase #2 $49.79   6.250%   $52.9019   $52.90   $52.90   $52.90  
  Purchase #3 $152.85   4.760%   $160.1257   $160.13   $160.15   $160.10  
  Purchase #4 $242.78   5.384%   $255.8513   $255.85   $255.85   $255.90  
  Purchase #5 $97.65   3.775%   $101.3363   $101.34   $101.35   $101.30  
  Purchase #6 $118.93   13.674%   $135.1925   $135.19   $135.20   $135.20  
  Purchase #7 $249.41   13.554%   $283.215   $283.22   $283.20   $283.20  
  7 purchase totals = $1,157.70       $1,263.3247   $1,263.33   $1,263.35   $1,263.30