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 $63.89   12.676%   $71.9887   $71.99   $72.00   $72.00  
  Purchase #2 $212.68   5.608%   $224.6071   $224.61   $224.60   $224.60  
  Purchase #3 $250.58   7.819%   $270.1729   $270.17   $270.15   $270.20  
  Purchase #4 $242.53   4.806%   $254.186   $254.19   $254.20   $254.20  
  Purchase #5 $39.83   13.751%   $45.307   $45.31   $45.30   $45.30  
  Purchase #6 $24.28   12.180%   $27.2373   $27.24   $27.25   $27.20  
  Purchase #7 $36.34   13.813%   $41.3596   $41.36   $41.35   $41.40  
  7 purchase totals = $870.13       $934.8586   $934.87   $934.85   $934.90