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 $141.94   12.562%   $159.7705   $159.77   $159.75   $159.80  
  Purchase #2 $106.37   10.309%   $117.3357   $117.34   $117.35   $117.30  
  Purchase #3 $73.38   12.356%   $82.4468   $82.45   $82.45   $82.40  
  Purchase #4 $31.78   10.836%   $35.2237   $35.22   $35.20   $35.20  
  Purchase #5 $219.54   6.456%   $233.7135   $233.71   $233.70   $233.70  
  Purchase #6 $69.86   6.848%   $74.644   $74.64   $74.65   $74.60  
  Purchase #7 $65.61   11.538%   $73.1801   $73.18   $73.20   $73.20  
  7 purchase totals = $708.48       $776.3143   $776.31   $776.30   $776.20