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 $69.74   8.829%   $75.8973   $75.90   $75.90   $75.90  
  Purchase #2 $170.95   7.603%   $183.9473   $183.95   $183.95   $183.90  
  Purchase #3 $81.79   7.165%   $87.6503   $87.65   $87.65   $87.70  
  Purchase #4 $16.59   9.865%   $18.2266   $18.23   $18.25   $18.20  
  Purchase #5 $239.87   7.516%   $257.8986   $257.90   $257.90   $257.90  
  Purchase #6 $60.37   11.691%   $67.4279   $67.43   $67.45   $67.40  
  Purchase #7 $153.71   9.662%   $168.5615   $168.56   $168.55   $168.60  
  7 purchase totals = $793.02       $859.6095   $859.62   $859.65   $859.60