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 $88.70   11.252%   $98.6805   $98.68   $98.70   $98.70  
  Purchase #2 $159.45   7.567%   $171.5156   $171.52   $171.50   $171.50  
  Purchase #3 $28.46   4.761%   $29.815   $29.82   $29.80   $29.80  
  Purchase #4 $250.44   8.691%   $272.2057   $272.21   $272.20   $272.20  
  Purchase #5 $222.76   3.494%   $230.5432   $230.54   $230.55   $230.50  
  Purchase #6 $5.96   5.123%   $6.2653   $6.27   $6.25   $6.30  
  Purchase #7 $224.51   4.494%   $234.5995   $234.60   $234.60   $234.60  
  7 purchase totals = $980.28       $1,043.6248   $1,043.64   $1,043.60   $1,043.60