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 $120.82   10.349%   $133.3237   $133.32   $133.30   $133.30  
  Purchase #2 $129.57   6.745%   $138.3095   $138.31   $138.30   $138.30  
  Purchase #3 $93.83   10.566%   $103.7441   $103.74   $103.75   $103.70  
  Purchase #4 $236.62   3.204%   $244.2013   $244.20   $244.20   $244.20  
  Purchase #5 $198.59   6.667%   $211.83   $211.83   $211.85   $211.80  
  Purchase #6 $21.26   3.238%   $21.9484   $21.95   $21.95   $21.90  
  Purchase #7 $200.92   10.647%   $222.312   $222.31   $222.30   $222.30  
  7 purchase totals = $1,001.61       $1,075.6690   $1,075.66   $1,075.65   $1,075.50