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 $67.55   13.378%   $76.5868   $76.59   $76.60   $76.60  
  Purchase #2 $160.68   8.517%   $174.3651   $174.37   $174.35   $174.40  
  Purchase #3 $202.75   13.300%   $229.7158   $229.72   $229.70   $229.70  
  Purchase #4 $225.66   8.351%   $244.5049   $244.50   $244.50   $244.50  
  Purchase #5 $135.62   13.291%   $153.6453   $153.65   $153.65   $153.60  
  Purchase #6 $119.50   5.634%   $126.2326   $126.23   $126.25   $126.20  
  Purchase #7 $245.71   12.814%   $277.1953   $277.20   $277.20   $277.20  
  7 purchase totals = $1,157.47       $1,282.2458   $1,282.26   $1,282.25   $1,282.20