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 $250.62   13.526%   $284.5189   $284.52   $284.50   $284.50  
  Purchase #2 $24.76   9.638%   $27.1464   $27.15   $27.15   $27.10  
  Purchase #3 $119.85   5.637%   $126.6059   $126.61   $126.60   $126.60  
  Purchase #4 $247.74   9.706%   $271.7856   $271.79   $271.80   $271.80  
  Purchase #5 $216.34   6.210%   $229.7747   $229.77   $229.75   $229.80  
  Purchase #6 $27.41   4.419%   $28.6212   $28.62   $28.60   $28.60  
  Purchase #7 $80.38   9.715%   $88.1889   $88.19   $88.20   $88.20  
  7 purchase totals = $967.10       $1,056.6416   $1,056.65   $1,056.60   $1,056.60