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 $214.43   11.601%   $239.306   $239.31   $239.30   $239.30  
  Purchase #2 $177.89   13.502%   $201.9087   $201.91   $201.90   $201.90  
  Purchase #3 $112.52   12.593%   $126.6896   $126.69   $126.70   $126.70  
  Purchase #4 $119.56   4.369%   $124.7836   $124.78   $124.80   $124.80  
  Purchase #5 $193.91   7.212%   $207.8948   $207.89   $207.90   $207.90  
  Purchase #6 $59.97   11.257%   $66.7208   $66.72   $66.70   $66.70  
  Purchase #7 $31.40   4.712%   $32.8796   $32.88   $32.90   $32.90  
  7 purchase totals = $909.68       $1,000.1831   $1,000.18   $1,000.20   $1,000.20