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 $246.80   5.357%   $260.0211   $260.02   $260.00   $260.00  
  Purchase #2 $206.78   12.216%   $232.0402   $232.04   $232.05   $232.00  
  Purchase #3 $202.75   3.663%   $210.1767   $210.18   $210.20   $210.20  
  Purchase #4 $83.27   10.108%   $91.6869   $91.69   $91.70   $91.70  
  Purchase #5 $247.90   6.731%   $264.5861   $264.59   $264.60   $264.60  
  Purchase #6 $236.75   8.278%   $256.3482   $256.35   $256.35   $256.30  
  Purchase #7 $219.38   13.467%   $248.9239   $248.92   $248.90   $248.90  
  7 purchase totals = $1,443.63       $1,563.7831   $1,563.79   $1,563.80   $1,563.70