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 $203.72   6.536%   $217.0351   $217.04   $217.05   $217.00  
  Purchase #2 $155.40   7.441%   $166.9633   $166.96   $166.95   $167.00  
  Purchase #3 $25.60   9.830%   $28.1165   $28.12   $28.10   $28.10  
  Purchase #4 $68.81   6.326%   $73.1629   $73.16   $73.15   $73.20  
  Purchase #5 $223.63   9.866%   $245.6933   $245.69   $245.70   $245.70  
  Purchase #6 $219.58   11.373%   $244.5528   $244.55   $244.55   $244.60  
  Purchase #7 $227.74   13.725%   $258.9973   $259.00   $259.00   $259.00  
  7 purchase totals = $1,124.48       $1,234.5212   $1,234.52   $1,234.50   $1,234.60