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 $220.56   13.831%   $251.0657   $251.07   $251.05   $251.10  
  Purchase #2 $206.64   12.104%   $231.6517   $231.65   $231.65   $231.70  
  Purchase #3 $69.48   9.812%   $76.2974   $76.30   $76.30   $76.30  
  Purchase #4 $51.56   12.517%   $58.0138   $58.01   $58.00   $58.00  
  Purchase #5 $217.85   13.119%   $246.4297   $246.43   $246.45   $246.40  
  Purchase #6 $209.68   6.839%   $224.02   $224.02   $224.00   $224.00  
  Purchase #7 $174.34   13.740%   $198.2943   $198.29   $198.30   $198.30  
  7 purchase totals = $1,150.11       $1,285.7726   $1,285.77   $1,285.75   $1,285.80