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 $177.26   8.582%   $192.4725   $192.47   $192.45   $192.50  
  Purchase #2 $125.91   6.846%   $134.5298   $134.53   $134.55   $134.50  
  Purchase #3 $46.56   12.730%   $52.4871   $52.49   $52.50   $52.50  
  Purchase #4 $247.62   7.391%   $265.9216   $265.92   $265.90   $265.90  
  Purchase #5 $59.47   7.249%   $63.781   $63.78   $63.80   $63.80  
  Purchase #6 $222.49   5.541%   $234.8182   $234.82   $234.80   $234.80  
  Purchase #7 $29.86   6.308%   $31.7436   $31.74   $31.75   $31.70  
  7 purchase totals = $909.17       $975.7538   $975.75   $975.75   $975.70