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 $233.77   8.865%   $254.4937   $254.49   $254.50   $254.50  
  Purchase #2 $122.78   4.815%   $128.6919   $128.69   $128.70   $128.70  
  Purchase #3 $24.43   6.596%   $26.0414   $26.04   $26.05   $26.00  
  Purchase #4 $105.83   11.272%   $117.7592   $117.76   $117.75   $117.80  
  Purchase #5 $169.26   13.118%   $191.4635   $191.46   $191.45   $191.50  
  Purchase #6 $191.76   5.745%   $202.7766   $202.78   $202.80   $202.80  
  Purchase #7 $20.43   5.575%   $21.569   $21.57   $21.55   $21.60  
  7 purchase totals = $868.26       $942.7953   $942.79   $942.80   $942.90