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 $237.77   3.679%   $246.5176   $246.52   $246.50   $246.50  
  Purchase #2 $76.85   6.162%   $81.5855   $81.59   $81.60   $81.60  
  Purchase #3 $20.44   3.640%   $21.184   $21.18   $21.20   $21.20  
  Purchase #4 $225.70   11.751%   $252.222   $252.22   $252.20   $252.20  
  Purchase #5 $241.82   6.143%   $256.675   $256.68   $256.70   $256.70  
  Purchase #6 $24.50   9.431%   $26.8106   $26.81   $26.80   $26.80  
  Purchase #7 $98.94   3.494%   $102.397   $102.40   $102.40   $102.40  
  7 purchase totals = $926.02       $987.3917   $987.40   $987.40   $987.40