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 $60.62   11.202%   $67.4107   $67.41   $67.40   $67.40  
  Purchase #2 $156.58   5.795%   $165.6538   $165.65   $165.65   $165.70  
  Purchase #3 $248.37   8.511%   $269.5088   $269.51   $269.50   $269.50  
  Purchase #4 $184.68   10.538%   $204.1416   $204.14   $204.15   $204.10  
  Purchase #5 $201.35   5.594%   $212.6135   $212.61   $212.60   $212.60  
  Purchase #6 $234.63   13.384%   $266.0329   $266.03   $266.05   $266.00  
  Purchase #7 $87.66   6.869%   $93.6814   $93.68   $93.70   $93.70  
  7 purchase totals = $1,173.89       $1,279.0427   $1,279.03   $1,279.05   $1,279.00