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 $246.34   6.654%   $262.7315   $262.73   $262.75   $262.70  
  Purchase #2 $118.29   13.255%   $133.9693   $133.97   $133.95   $134.00  
  Purchase #3 $97.47   11.276%   $108.4607   $108.46   $108.45   $108.50  
  Purchase #4 $195.30   11.312%   $217.3923   $217.39   $217.40   $217.40  
  Purchase #5 $110.59   6.362%   $117.6257   $117.63   $117.65   $117.60  
  Purchase #6 $84.76   7.818%   $91.3865   $91.39   $91.40   $91.40  
  Purchase #7 $142.96   13.856%   $162.7685   $162.77   $162.75   $162.80  
  7 purchase totals = $995.71       $1,094.3345   $1,094.34   $1,094.35   $1,094.40