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 $53.67   8.441%   $58.2003   $58.20   $58.20   $58.20  
  Purchase #2 $194.85   7.183%   $208.8461   $208.85   $208.85   $208.80  
  Purchase #3 $243.93   8.760%   $265.2983   $265.30   $265.30   $265.30  
  Purchase #4 $227.74   3.864%   $236.5399   $236.54   $236.55   $236.50  
  Purchase #5 $152.75   8.130%   $165.1686   $165.17   $165.15   $165.20  
  Purchase #6 $140.52   7.245%   $150.7007   $150.70   $150.70   $150.70  
  Purchase #7 $67.74   12.813%   $76.4195   $76.42   $76.40   $76.40  
  7 purchase totals = $1,081.20       $1,161.1734   $1,161.18   $1,161.15   $1,161.10