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 $246.68   9.290%   $269.5966   $269.60   $269.60   $269.60  
  Purchase #2 $48.59   11.729%   $54.2891   $54.29   $54.30   $54.30  
  Purchase #3 $206.77   12.578%   $232.7775   $232.78   $232.80   $232.80  
  Purchase #4 $235.69   12.329%   $264.7482   $264.75   $264.75   $264.70  
  Purchase #5 $169.75   8.261%   $183.773   $183.77   $183.75   $183.80  
  Purchase #6 $235.40   10.795%   $260.8114   $260.81   $260.80   $260.80  
  Purchase #7 $19.33   3.133%   $19.9356   $19.94   $19.95   $19.90  
  7 purchase totals = $1,162.21       $1,285.9314   $1,285.94   $1,285.95   $1,285.90