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 $179.26   13.264%   $203.037   $203.04   $203.05   $203.00  
  Purchase #2 $215.61   7.107%   $230.9334   $230.93   $230.95   $230.90  
  Purchase #3 $59.65   12.585%   $67.157   $67.16   $67.15   $67.20  
  Purchase #4 $132.61   3.272%   $136.949   $136.95   $136.95   $136.90  
  Purchase #5 $224.27   11.125%   $249.22   $249.22   $249.20   $249.20  
  Purchase #6 $247.29   3.443%   $255.8042   $255.80   $255.80   $255.80  
  Purchase #7 $120.82   12.505%   $135.9285   $135.93   $135.95   $135.90  
  7 purchase totals = $1,179.51       $1,279.0291   $1,279.03   $1,279.05   $1,278.90