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 $192.34   6.773%   $205.3672   $205.37   $205.35   $205.40  
  Purchase #2 $15.76   7.395%   $16.9255   $16.93   $16.95   $16.90  
  Purchase #3 $20.80   13.285%   $23.5633   $23.56   $23.55   $23.60  
  Purchase #4 $23.33   6.621%   $24.8747   $24.87   $24.85   $24.90  
  Purchase #5 $49.33   6.580%   $52.5759   $52.58   $52.60   $52.60  
  Purchase #6 $197.80   11.334%   $220.2187   $220.22   $220.20   $220.20  
  Purchase #7 $208.82   8.419%   $226.4006   $226.40   $226.40   $226.40  
  7 purchase totals = $708.18       $769.9259   $769.93   $769.90   $770.00