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 $235.70   13.604%   $267.7646   $267.76   $267.75   $267.80  
  Purchase #2 $88.93   8.804%   $96.7594   $96.76   $96.75   $96.80  
  Purchase #3 $238.57   5.584%   $251.8917   $251.89   $251.90   $251.90  
  Purchase #4 $166.94   8.654%   $181.387   $181.39   $181.40   $181.40  
  Purchase #5 $180.53   12.171%   $202.5023   $202.50   $202.50   $202.50  
  Purchase #6 $139.96   12.457%   $157.3948   $157.39   $157.40   $157.40  
  Purchase #7 $104.68   3.310%   $108.1449   $108.14   $108.15   $108.10  
  7 purchase totals = $1,155.31       $1,265.8447   $1,265.83   $1,265.85   $1,265.90