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 $149.93   7.555%   $161.2572   $161.26   $161.25   $161.30  
  Purchase #2 $157.97   9.151%   $172.4258   $172.43   $172.45   $172.40  
  Purchase #3 $84.61   4.722%   $88.6053   $88.61   $88.60   $88.60  
  Purchase #4 $69.56   3.826%   $72.2214   $72.22   $72.20   $72.20  
  Purchase #5 $47.65   9.517%   $52.1849   $52.18   $52.20   $52.20  
  Purchase #6 $144.59   6.452%   $153.9189   $153.92   $153.90   $153.90  
  Purchase #7 $228.73   5.413%   $241.1112   $241.11   $241.10   $241.10  
  7 purchase totals = $883.04       $941.7247   $941.73   $941.70   $941.70