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 $85.54   10.437%   $94.4678   $94.47   $94.45   $94.50  
  Purchase #2 $234.76   6.595%   $250.2424   $250.24   $250.25   $250.20  
  Purchase #3 $49.85   13.414%   $56.5369   $56.54   $56.55   $56.50  
  Purchase #4 $207.82   10.615%   $229.8801   $229.88   $229.90   $229.90  
  Purchase #5 $60.84   13.437%   $69.0151   $69.02   $69.00   $69.00  
  Purchase #6 $232.85   9.340%   $254.5982   $254.60   $254.60   $254.60  
  Purchase #7 $170.95   9.470%   $187.139   $187.14   $187.15   $187.10  
  7 purchase totals = $1,042.61       $1,141.8795   $1,141.89   $1,141.90   $1,141.80