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 $179.25   13.118%   $202.764   $202.76   $202.75   $202.80  
  Purchase #2 $14.65   10.687%   $16.2156   $16.22   $16.20   $16.20  
  Purchase #3 $180.46   12.719%   $203.4127   $203.41   $203.40   $203.40  
  Purchase #4 $75.43   4.691%   $78.9684   $78.97   $78.95   $79.00  
  Purchase #5 $212.66   12.496%   $239.234   $239.23   $239.25   $239.20  
  Purchase #6 $205.96   13.439%   $233.639   $233.64   $233.65   $233.60  
  Purchase #7 $82.49   6.401%   $87.7702   $87.77   $87.75   $87.80  
  7 purchase totals = $950.90       $1,062.0039   $1,062.00   $1,061.95   $1,062.00