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 $96.76   6.719%   $103.2613   $103.26   $103.25   $103.30  
  Purchase #2 $23.98   5.628%   $25.3296   $25.33   $25.35   $25.30  
  Purchase #3 $58.65   10.774%   $64.969   $64.97   $64.95   $65.00  
  Purchase #4 $88.25   12.624%   $99.3907   $99.39   $99.40   $99.40  
  Purchase #5 $195.32   5.458%   $205.9806   $205.98   $206.00   $206.00  
  Purchase #6 $232.73   6.616%   $248.1274   $248.13   $248.15   $248.10  
  Purchase #7 $237.62   9.786%   $260.8735   $260.87   $260.85   $260.90  
  7 purchase totals = $933.31       $1,007.9321   $1,007.93   $1,007.95   $1,008.00