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 $53.67   10.744%   $59.4363   $59.44   $59.45   $59.40  
  Purchase #2 $142.99   10.704%   $158.2956   $158.30   $158.30   $158.30  
  Purchase #3 $175.98   13.414%   $199.586   $199.59   $199.60   $199.60  
  Purchase #4 $203.53   8.191%   $220.2011   $220.20   $220.20   $220.20  
  Purchase #5 $61.83   7.640%   $66.5538   $66.55   $66.55   $66.60  
  Purchase #6 $169.70   11.619%   $189.4174   $189.42   $189.40   $189.40  
  Purchase #7 $62.35   6.788%   $66.5823   $66.58   $66.60   $66.60  
  7 purchase totals = $870.05       $960.0725   $960.08   $960.10   $960.10