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 $180.96   13.836%   $205.9976   $206.00   $206.00   $206.00  
  Purchase #2 $90.62   7.662%   $97.5633   $97.56   $97.55   $97.60  
  Purchase #3 $223.46   10.780%   $247.549   $247.55   $247.55   $247.50  
  Purchase #4 $112.52   6.492%   $119.8248   $119.82   $119.80   $119.80  
  Purchase #5 $55.59   10.800%   $61.5937   $61.59   $61.60   $61.60  
  Purchase #6 $93.60   11.305%   $104.1815   $104.18   $104.20   $104.20  
  Purchase #7 $182.34   8.619%   $198.0559   $198.06   $198.05   $198.10  
  7 purchase totals = $939.09       $1,034.7658   $1,034.76   $1,034.75   $1,034.80