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 $131.48   13.298%   $148.9642   $148.96   $148.95   $149.00  
  Purchase #2 $122.76   8.871%   $133.65   $133.65   $133.65   $133.70  
  Purchase #3 $179.44   11.721%   $200.4722   $200.47   $200.45   $200.50  
  Purchase #4 $88.59   6.210%   $94.0914   $94.09   $94.10   $94.10  
  Purchase #5 $189.91   8.345%   $205.758   $205.76   $205.75   $205.80  
  Purchase #6 $20.32   5.756%   $21.4896   $21.49   $21.50   $21.50  
  Purchase #7 $173.33   9.171%   $189.2261   $189.23   $189.25   $189.20  
  7 purchase totals = $905.83       $993.6515   $993.65   $993.65   $993.80