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 $228.95   5.284%   $241.0477   $241.05   $241.05   $241.00  
  Purchase #2 $195.70   12.264%   $219.7006   $219.70   $219.70   $219.70  
  Purchase #3 $231.41   5.526%   $244.1977   $244.20   $244.20   $244.20  
  Purchase #4 $38.77   5.132%   $40.7597   $40.76   $40.75   $40.80  
  Purchase #5 $93.71   9.635%   $102.739   $102.74   $102.75   $102.70  
  Purchase #6 $36.38   13.466%   $41.2789   $41.28   $41.30   $41.30  
  Purchase #7 $128.63   6.395%   $136.8559   $136.86   $136.85   $136.90  
  7 purchase totals = $953.55       $1,026.5795   $1,026.59   $1,026.60   $1,026.60