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 $184.86   11.815%   $206.7012   $206.70   $206.70   $206.70  
  Purchase #2 $212.90   13.308%   $241.2327   $241.23   $241.25   $241.20  
  Purchase #3 $65.36   6.164%   $69.3888   $69.39   $69.40   $69.40  
  Purchase #4 $47.82   13.395%   $54.2255   $54.23   $54.25   $54.20  
  Purchase #5 $162.62   11.306%   $181.0058   $181.01   $181.00   $181.00  
  Purchase #6 $197.51   5.478%   $208.3296   $208.33   $208.35   $208.30  
  Purchase #7 $121.42   12.296%   $136.3498   $136.35   $136.35   $136.30  
  7 purchase totals = $992.49       $1,097.2334   $1,097.24   $1,097.30   $1,097.10