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 $238.83   6.493%   $254.3372   $254.34   $254.35   $254.30  
  Purchase #2 $47.69   4.204%   $49.6949   $49.69   $49.70   $49.70  
  Purchase #3 $229.95   13.269%   $260.4621   $260.46   $260.45   $260.50  
  Purchase #4 $169.72   8.816%   $184.6825   $184.68   $184.70   $184.70  
  Purchase #5 $165.91   6.259%   $176.2943   $176.29   $176.30   $176.30  
  Purchase #6 $105.47   5.648%   $111.4269   $111.43   $111.45   $111.40  
  Purchase #7 $7.73   7.437%   $8.3049   $8.30   $8.30   $8.30  
  7 purchase totals = $965.30       $1,045.2028   $1,045.19   $1,045.25   $1,045.20