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 $202.52   13.576%   $230.0141   $230.01   $230.00   $230.00  
  Purchase #2 $22.46   5.610%   $23.72   $23.72   $23.70   $23.70  
  Purchase #3 $126.81   6.588%   $135.1642   $135.16   $135.15   $135.20  
  Purchase #4 $209.66   5.626%   $221.4555   $221.46   $221.45   $221.50  
  Purchase #5 $244.68   7.753%   $263.65   $263.65   $263.65   $263.70  
  Purchase #6 $200.61   4.709%   $210.0567   $210.06   $210.05   $210.10  
  Purchase #7 $249.91   3.643%   $259.0142   $259.01   $259.00   $259.00  
  7 purchase totals = $1,256.65       $1,343.0747   $1,343.07   $1,343.00   $1,343.20