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 $110.80   13.678%   $125.9552   $125.96   $125.95   $126.00  
  Purchase #2 $190.86   4.563%   $199.5689   $199.57   $199.55   $199.60  
  Purchase #3 $194.59   5.406%   $205.1095   $205.11   $205.10   $205.10  
  Purchase #4 $113.57   12.454%   $127.714   $127.71   $127.70   $127.70  
  Purchase #5 $42.77   12.236%   $48.0033   $48.00   $48.00   $48.00  
  Purchase #6 $191.39   11.512%   $213.4228   $213.42   $213.40   $213.40  
  Purchase #7 $70.72   5.298%   $74.4667   $74.47   $74.45   $74.50  
  7 purchase totals = $914.70       $994.2404   $994.24   $994.15   $994.30