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 $215.49   5.265%   $226.8355   $226.84   $226.85   $226.80  
  Purchase #2 $160.64   3.549%   $166.3411   $166.34   $166.35   $166.30  
  Purchase #3 $105.33   5.548%   $111.1737   $111.17   $111.15   $111.20  
  Purchase #4 $184.66   9.216%   $201.6783   $201.68   $201.70   $201.70  
  Purchase #5 $232.81   9.743%   $255.4927   $255.49   $255.50   $255.50  
  Purchase #6 $162.93   6.720%   $173.8789   $173.88   $173.90   $173.90  
  Purchase #7 $171.63   7.402%   $184.3341   $184.33   $184.35   $184.30  
  7 purchase totals = $1,233.49       $1,319.7343   $1,319.73   $1,319.80   $1,319.70