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 $231.79   4.163%   $241.4394   $241.44   $241.45   $241.40  
  Purchase #2 $30.56   13.387%   $34.6511   $34.65   $34.65   $34.70  
  Purchase #3 $204.89   13.562%   $232.6772   $232.68   $232.70   $232.70  
  Purchase #4 $95.33   8.159%   $103.108   $103.11   $103.10   $103.10  
  Purchase #5 $210.78   7.589%   $226.7761   $226.78   $226.80   $226.80  
  Purchase #6 $6.95   7.324%   $7.459   $7.46   $7.45   $7.50  
  Purchase #7 $72.71   4.264%   $75.8104   $75.81   $75.80   $75.80  
  7 purchase totals = $853.01       $921.9212   $921.93   $921.95   $922.00