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 $207.76   10.571%   $229.7223   $229.72   $229.70   $229.70  
  Purchase #2 $138.37   8.398%   $149.9903   $149.99   $150.00   $150.00  
  Purchase #3 $60.65   7.347%   $65.106   $65.11   $65.10   $65.10  
  Purchase #4 $223.99   8.145%   $242.234   $242.23   $242.25   $242.20  
  Purchase #5 $102.25   10.253%   $112.7337   $112.73   $112.75   $112.70  
  Purchase #6 $112.75   4.149%   $117.428   $117.43   $117.45   $117.40  
  Purchase #7 $182.30   4.274%   $190.0915   $190.09   $190.10   $190.10  
  7 purchase totals = $1,028.07       $1,107.3058   $1,107.30   $1,107.35   $1,107.20