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 $233.60   8.811%   $254.1825   $254.18   $254.20   $254.20  
  Purchase #2 $137.87   7.313%   $147.9524   $147.95   $147.95   $148.00  
  Purchase #3 $86.86   6.838%   $92.7995   $92.80   $92.80   $92.80  
  Purchase #4 $245.80   8.762%   $267.337   $267.34   $267.35   $267.30  
  Purchase #5 $32.70   12.683%   $36.8473   $36.85   $36.85   $36.80  
  Purchase #6 $59.65   11.459%   $66.4853   $66.49   $66.50   $66.50  
  Purchase #7 $70.32   13.283%   $79.6606   $79.66   $79.65   $79.70  
  7 purchase totals = $866.80       $945.2646   $945.27   $945.30   $945.30