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 $41.71   5.117%   $43.8443   $43.84   $43.85   $43.80  
  Purchase #2 $146.60   7.536%   $157.6478   $157.65   $157.65   $157.60  
  Purchase #3 $196.62   7.774%   $211.9052   $211.91   $211.90   $211.90  
  Purchase #4 $211.35   13.378%   $239.6244   $239.62   $239.60   $239.60  
  Purchase #5 $129.68   9.327%   $141.7753   $141.78   $141.80   $141.80  
  Purchase #6 $144.30   5.306%   $151.9566   $151.96   $151.95   $152.00  
  Purchase #7 $21.59   12.341%   $24.2544   $24.25   $24.25   $24.30  
  7 purchase totals = $891.85       $971.0080   $971.01   $971.00   $971.00