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 $118.70   4.815%   $124.4154   $124.42   $124.40   $124.40  
  Purchase #2 $89.76   10.549%   $99.2288   $99.23   $99.25   $99.20  
  Purchase #3 $146.35   5.573%   $154.5061   $154.51   $154.50   $154.50  
  Purchase #4 $202.98   9.139%   $221.5303   $221.53   $221.55   $221.50  
  Purchase #5 $111.57   13.385%   $126.5036   $126.50   $126.50   $126.50  
  Purchase #6 $166.67   11.485%   $185.812   $185.81   $185.80   $185.80  
  Purchase #7 $165.46   13.741%   $188.1959   $188.20   $188.20   $188.20  
  7 purchase totals = $1,001.49       $1,100.1921   $1,100.20   $1,100.20   $1,100.10