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 $205.69   9.155%   $224.5209   $224.52   $224.50   $224.50  
  Purchase #2 $84.69   9.330%   $92.5916   $92.59   $92.60   $92.60  
  Purchase #3 $94.64   12.839%   $106.7908   $106.79   $106.80   $106.80  
  Purchase #4 $92.69   9.269%   $101.2814   $101.28   $101.30   $101.30  
  Purchase #5 $89.25   3.826%   $92.6647   $92.66   $92.65   $92.70  
  Purchase #6 $211.91   11.497%   $236.2733   $236.27   $236.25   $236.30  
  Purchase #7 $173.89   6.212%   $184.692   $184.69   $184.70   $184.70  
  7 purchase totals = $952.76       $1,038.8147   $1,038.80   $1,038.80   $1,038.90