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 $245.70   6.639%   $262.012   $262.01   $262.00   $262.00  
  Purchase #2 $12.58   8.830%   $13.6908   $13.69   $13.70   $13.70  
  Purchase #3 $41.53   5.483%   $43.8071   $43.81   $43.80   $43.80  
  Purchase #4 $197.93   8.419%   $214.5937   $214.59   $214.60   $214.60  
  Purchase #5 $40.35   7.623%   $43.4259   $43.43   $43.45   $43.40  
  Purchase #6 $6.43   3.701%   $6.668   $6.67   $6.65   $6.70  
  Purchase #7 $142.94   4.316%   $149.1093   $149.11   $149.10   $149.10  
  7 purchase totals = $687.46       $733.3068   $733.31   $733.30   $733.30