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 $197.67   13.157%   $223.6774   $223.68   $223.70   $223.70  
  Purchase #2 $94.42   10.388%   $104.2283   $104.23   $104.25   $104.20  
  Purchase #3 $86.43   7.862%   $93.2251   $93.23   $93.25   $93.20  
  Purchase #4 $38.52   7.248%   $41.3119   $41.31   $41.30   $41.30  
  Purchase #5 $67.57   12.550%   $76.05   $76.05   $76.05   $76.10  
  Purchase #6 $247.42   12.263%   $277.7611   $277.76   $277.75   $277.80  
  Purchase #7 $121.28   10.639%   $134.183   $134.18   $134.20   $134.20  
  7 purchase totals = $853.31       $950.4368   $950.44   $950.50   $950.50