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 $234.66   13.210%   $265.6586   $265.66   $265.65   $265.70  
  Purchase #2 $109.74   8.317%   $118.8671   $118.87   $118.85   $118.90  
  Purchase #3 $218.74   11.555%   $244.0154   $244.02   $244.00   $244.00  
  Purchase #4 $163.72   9.256%   $178.8739   $178.87   $178.85   $178.90  
  Purchase #5 $42.67   12.545%   $48.023   $48.02   $48.00   $48.00  
  Purchase #6 $92.80   7.197%   $99.4788   $99.48   $99.50   $99.50  
  Purchase #7 $99.70   8.614%   $108.2882   $108.29   $108.30   $108.30  
  7 purchase totals = $962.03       $1,063.2050   $1,063.21   $1,063.15   $1,063.30