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 $221.97   9.597%   $243.2725   $243.27   $243.25   $243.30  
  Purchase #2 $140.69   7.117%   $150.7029   $150.70   $150.70   $150.70  
  Purchase #3 $39.37   11.252%   $43.7999   $43.80   $43.80   $43.80  
  Purchase #4 $123.73   11.848%   $138.3895   $138.39   $138.40   $138.40  
  Purchase #5 $99.38   8.156%   $107.4854   $107.49   $107.50   $107.50  
  Purchase #6 $93.95   10.471%   $103.7875   $103.79   $103.80   $103.80  
  Purchase #7 $240.36   10.634%   $265.9199   $265.92   $265.90   $265.90  
  7 purchase totals = $959.45       $1,053.3576   $1,053.36   $1,053.35   $1,053.40