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 $78.41   10.607%   $86.7269   $86.73   $86.75   $86.70  
  Purchase #2 $83.54   4.719%   $87.4823   $87.48   $87.50   $87.50  
  Purchase #3 $93.43   6.181%   $99.2049   $99.20   $99.20   $99.20  
  Purchase #4 $212.45   13.558%   $241.254   $241.25   $241.25   $241.30  
  Purchase #5 $73.46   3.215%   $75.8217   $75.82   $75.80   $75.80  
  Purchase #6 $180.96   8.161%   $195.7281   $195.73   $195.75   $195.70  
  Purchase #7 $225.94   6.564%   $240.7707   $240.77   $240.75   $240.80  
  7 purchase totals = $948.19       $1,026.9886   $1,026.98   $1,027.00   $1,027.00