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 $65.47   12.456%   $73.6249   $73.62   $73.60   $73.60  
  Purchase #2 $154.62   6.389%   $164.4987   $164.50   $164.50   $164.50  
  Purchase #3 $164.76   11.293%   $183.3663   $183.37   $183.35   $183.40  
  Purchase #4 $168.64   12.799%   $190.2242   $190.22   $190.20   $190.20  
  Purchase #5 $36.52   11.725%   $40.802   $40.80   $40.80   $40.80  
  Purchase #6 $184.45   9.328%   $201.6555   $201.66   $201.65   $201.70  
  Purchase #7 $145.97   5.226%   $153.5984   $153.60   $153.60   $153.60  
  7 purchase totals = $920.43       $1,007.7700   $1,007.77   $1,007.70   $1,007.80