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 $221.46   11.495%   $246.9168   $246.92   $246.90   $246.90  
  Purchase #2 $85.52   9.133%   $93.3305   $93.33   $93.35   $93.30  
  Purchase #3 $112.91   12.181%   $126.6636   $126.66   $126.65   $126.70  
  Purchase #4 $227.30   11.571%   $253.6009   $253.60   $253.60   $253.60  
  Purchase #5 $196.63   13.656%   $223.4818   $223.48   $223.50   $223.50  
  Purchase #6 $55.35   11.792%   $61.8769   $61.88   $61.90   $61.90  
  Purchase #7 $234.48   5.238%   $246.7621   $246.76   $246.75   $246.80  
  7 purchase totals = $1,133.65       $1,252.6326   $1,252.63   $1,252.65   $1,252.70