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 $136.77   7.620%   $147.1919   $147.19   $147.20   $147.20  
  Purchase #2 $32.87   5.871%   $34.7998   $34.80   $34.80   $34.80  
  Purchase #3 $57.25   11.286%   $63.7112   $63.71   $63.70   $63.70  
  Purchase #4 $177.46   13.405%   $201.2485   $201.25   $201.25   $201.20  
  Purchase #5 $75.47   8.820%   $82.1265   $82.13   $82.15   $82.10  
  Purchase #6 $226.46   5.120%   $238.0548   $238.05   $238.05   $238.10  
  Purchase #7 $161.75   7.645%   $174.1158   $174.12   $174.10   $174.10  
  7 purchase totals = $868.03       $941.2485   $941.25   $941.25   $941.20