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 $207.26   8.252%   $224.3631   $224.36   $224.35   $224.40  
  Purchase #2 $72.46   3.540%   $75.0251   $75.03   $75.05   $75.00  
  Purchase #3 $50.78   7.867%   $54.7749   $54.77   $54.75   $54.80  
  Purchase #4 $161.86   3.594%   $167.6772   $167.68   $167.70   $167.70  
  Purchase #5 $142.69   7.714%   $153.6971   $153.70   $153.70   $153.70  
  Purchase #6 $222.47   6.517%   $236.9684   $236.97   $236.95   $237.00  
  Purchase #7 $86.93   8.148%   $94.0131   $94.01   $94.00   $94.00  
  7 purchase totals = $944.45       $1,006.5189   $1,006.52   $1,006.50   $1,006.60