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 $92.68   13.490%   $105.1825   $105.18   $105.20   $105.20  
  Purchase #2 $130.81   11.308%   $145.602   $145.60   $145.60   $145.60  
  Purchase #3 $53.33   8.647%   $57.9414   $57.94   $57.95   $57.90  
  Purchase #4 $159.67   7.271%   $171.2796   $171.28   $171.30   $171.30  
  Purchase #5 $118.86   13.859%   $135.3328   $135.33   $135.35   $135.30  
  Purchase #6 $233.27   5.708%   $246.5851   $246.59   $246.60   $246.60  
  Purchase #7 $153.74   5.812%   $162.6754   $162.68   $162.70   $162.70  
  7 purchase totals = $942.36       $1,024.5988   $1,024.60   $1,024.70   $1,024.60