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 $216.85   4.210%   $225.9794   $225.98   $226.00   $226.00  
  Purchase #2 $135.61   8.370%   $146.9606   $146.96   $146.95   $147.00  
  Purchase #3 $184.79   13.758%   $210.2134   $210.21   $210.20   $210.20  
  Purchase #4 $165.95   5.675%   $175.3677   $175.37   $175.35   $175.40  
  Purchase #5 $224.84   9.851%   $246.989   $246.99   $247.00   $247.00  
  Purchase #6 $128.64   10.112%   $141.6481   $141.65   $141.65   $141.60  
  Purchase #7 $112.36   6.492%   $119.6544   $119.65   $119.65   $119.70  
  7 purchase totals = $1,169.04       $1,266.8126   $1,266.81   $1,266.80   $1,266.90