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 $249.51   6.593%   $265.9602   $265.96   $265.95   $266.00  
  Purchase #2 $58.25   12.550%   $65.5604   $65.56   $65.55   $65.60  
  Purchase #3 $208.50   4.171%   $217.1965   $217.20   $217.20   $217.20  
  Purchase #4 $219.31   4.222%   $228.5693   $228.57   $228.55   $228.60  
  Purchase #5 $214.77   8.443%   $232.903   $232.90   $232.90   $232.90  
  Purchase #6 $221.50   7.546%   $238.2144   $238.21   $238.20   $238.20  
  Purchase #7 $192.83   5.215%   $202.8861   $202.89   $202.90   $202.90  
  7 purchase totals = $1,364.67       $1,451.2899   $1,451.29   $1,451.25   $1,451.40