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 $83.49   11.788%   $93.3318   $93.33   $93.35   $93.30  
  Purchase #2 $171.67   8.153%   $185.6663   $185.67   $185.65   $185.70  
  Purchase #3 $241.95   9.508%   $264.9546   $264.95   $264.95   $265.00  
  Purchase #4 $5.98   12.623%   $6.7349   $6.73   $6.75   $6.70  
  Purchase #5 $236.75   11.174%   $263.2044   $263.20   $263.20   $263.20  
  Purchase #6 $127.30   10.197%   $140.2808   $140.28   $140.30   $140.30  
  Purchase #7 $161.42   12.123%   $180.9889   $180.99   $181.00   $181.00  
  7 purchase totals = $1,028.56       $1,135.1617   $1,135.15   $1,135.20   $1,135.20