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 $63.60   12.815%   $71.7503   $71.75   $71.75   $71.80  
  Purchase #2 $209.83   12.326%   $235.6936   $235.69   $235.70   $235.70  
  Purchase #3 $124.48   7.424%   $133.7214   $133.72   $133.70   $133.70  
  Purchase #4 $106.82   4.582%   $111.7145   $111.71   $111.70   $111.70  
  Purchase #5 $186.72   6.182%   $198.263   $198.26   $198.25   $198.30  
  Purchase #6 $156.38   8.420%   $169.5472   $169.55   $169.55   $169.50  
  Purchase #7 $161.81   3.852%   $168.0429   $168.04   $168.05   $168.00  
  7 purchase totals = $1,009.64       $1,088.7329   $1,088.72   $1,088.70   $1,088.70