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 $214.96   12.563%   $241.9654   $241.97   $241.95   $242.00  
  Purchase #2 $229.54   13.577%   $260.7046   $260.70   $260.70   $260.70  
  Purchase #3 $203.55   7.598%   $219.0157   $219.02   $219.00   $219.00  
  Purchase #4 $102.27   9.622%   $112.1104   $112.11   $112.10   $112.10  
  Purchase #5 $79.60   6.170%   $84.5113   $84.51   $84.50   $84.50  
  Purchase #6 $196.82   12.801%   $222.0149   $222.01   $222.00   $222.00  
  Purchase #7 $122.59   8.558%   $133.0813   $133.08   $133.10   $133.10  
  7 purchase totals = $1,149.33       $1,273.4036   $1,273.40   $1,273.35   $1,273.40