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 $86.35   10.701%   $95.5903   $95.59   $95.60   $95.60  
  Purchase #2 $250.98   13.716%   $285.4044   $285.40   $285.40   $285.40  
  Purchase #3 $63.64   12.331%   $71.4874   $71.49   $71.50   $71.50  
  Purchase #4 $28.63   5.649%   $30.2473   $30.25   $30.25   $30.20  
  Purchase #5 $96.50   5.700%   $102.0005   $102.00   $102.00   $102.00  
  Purchase #6 $175.90   8.767%   $191.3212   $191.32   $191.30   $191.30  
  Purchase #7 $207.75   10.303%   $229.1545   $229.15   $229.15   $229.20  
  7 purchase totals = $909.75       $1,005.2056   $1,005.20   $1,005.20   $1,005.20