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 $228.90   10.231%   $252.3188   $252.32   $252.30   $252.30  
  Purchase #2 $83.86   13.268%   $94.9865   $94.99   $95.00   $95.00  
  Purchase #3 $47.90   8.146%   $51.8019   $51.80   $51.80   $51.80  
  Purchase #4 $16.89   8.395%   $18.3079   $18.31   $18.30   $18.30  
  Purchase #5 $170.90   10.728%   $189.2342   $189.23   $189.25   $189.20  
  Purchase #6 $147.39   13.733%   $167.6311   $167.63   $167.65   $167.60  
  Purchase #7 $35.44   11.750%   $39.6042   $39.60   $39.60   $39.60  
  7 purchase totals = $731.28       $813.8846   $813.88   $813.90   $813.80