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 $245.69   7.455%   $264.0062   $264.01   $264.00   $264.00  
  Purchase #2 $225.60   8.141%   $243.9661   $243.97   $243.95   $244.00  
  Purchase #3 $13.58   7.253%   $14.565   $14.57   $14.55   $14.60  
  Purchase #4 $231.82   12.153%   $259.9931   $259.99   $260.00   $260.00  
  Purchase #5 $45.51   13.335%   $51.5788   $51.58   $51.60   $51.60  
  Purchase #6 $31.83   4.748%   $33.3413   $33.34   $33.35   $33.30  
  Purchase #7 $75.66   9.545%   $82.8817   $82.88   $82.90   $82.90  
  7 purchase totals = $869.69       $950.3322   $950.34   $950.35   $950.40