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 $208.82   8.387%   $226.3337   $226.33   $226.35   $226.30  
  Purchase #2 $225.35   9.296%   $246.2985   $246.30   $246.30   $246.30  
  Purchase #3 $23.52   8.855%   $25.6027   $25.60   $25.60   $25.60  
  Purchase #4 $91.91   12.288%   $103.2039   $103.20   $103.20   $103.20  
  Purchase #5 $193.70   13.441%   $219.7352   $219.74   $219.75   $219.70  
  Purchase #6 $93.78   7.481%   $100.7957   $100.80   $100.80   $100.80  
  Purchase #7 $83.59   13.362%   $94.7593   $94.76   $94.75   $94.80  
  7 purchase totals = $920.67       $1,016.7290   $1,016.73   $1,016.75   $1,016.70