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 $248.72   5.676%   $262.8373   $262.84   $262.85   $262.80  
  Purchase #2 $53.34   12.480%   $59.9968   $60.00   $60.00   $60.00  
  Purchase #3 $147.30   13.477%   $167.1516   $167.15   $167.15   $167.20  
  Purchase #4 $54.67   3.112%   $56.3713   $56.37   $56.35   $56.40  
  Purchase #5 $170.75   8.342%   $184.994   $184.99   $185.00   $185.00  
  Purchase #6 $127.44   4.621%   $133.329   $133.33   $133.35   $133.30  
  Purchase #7 $43.62   6.586%   $46.4928   $46.49   $46.50   $46.50  
  7 purchase totals = $845.84       $911.1728   $911.17   $911.20   $911.20