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 $44.83   13.111%   $50.7077   $50.71   $50.70   $50.70  
  Purchase #2 $219.60   9.598%   $240.6772   $240.68   $240.70   $240.70  
  Purchase #3 $214.40   12.819%   $241.8839   $241.88   $241.90   $241.90  
  Purchase #4 $120.50   10.616%   $133.2923   $133.29   $133.30   $133.30  
  Purchase #5 $12.67   10.688%   $14.0242   $14.02   $14.00   $14.00  
  Purchase #6 $164.51   3.457%   $170.1971   $170.20   $170.20   $170.20  
  Purchase #7 $71.77   5.747%   $75.8946   $75.89   $75.90   $75.90  
  7 purchase totals = $848.28       $926.6770   $926.67   $926.70   $926.70