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 $232.76   3.656%   $241.2697   $241.27   $241.25   $241.30  
  Purchase #2 $172.67   4.143%   $179.8237   $179.82   $179.80   $179.80  
  Purchase #3 $98.67   10.776%   $109.3027   $109.30   $109.30   $109.30  
  Purchase #4 $182.32   6.791%   $194.7014   $194.70   $194.70   $194.70  
  Purchase #5 $207.46   5.851%   $219.5985   $219.60   $219.60   $219.60  
  Purchase #6 $24.33   10.785%   $26.954   $26.95   $26.95   $27.00  
  Purchase #7 $200.51   13.507%   $227.5929   $227.59   $227.60   $227.60  
  7 purchase totals = $1,118.72       $1,199.2429   $1,199.23   $1,199.20   $1,199.30