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 $239.90   9.722%   $263.2231   $263.22   $263.20   $263.20  
  Purchase #2 $81.74   5.192%   $85.9839   $85.98   $86.00   $86.00  
  Purchase #3 $112.54   7.332%   $120.7914   $120.79   $120.80   $120.80  
  Purchase #4 $178.40   10.723%   $197.5298   $197.53   $197.55   $197.50  
  Purchase #5 $24.86   6.372%   $26.4441   $26.44   $26.45   $26.40  
  Purchase #6 $112.95   10.711%   $125.0481   $125.05   $125.05   $125.00  
  Purchase #7 $194.76   4.494%   $203.5125   $203.51   $203.50   $203.50  
  7 purchase totals = $945.15       $1,022.5329   $1,022.52   $1,022.55   $1,022.40