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 $186.92   9.113%   $203.954   $203.95   $203.95   $204.00  
  Purchase #2 $85.87   3.872%   $89.1949   $89.19   $89.20   $89.20  
  Purchase #3 $143.32   7.178%   $153.6075   $153.61   $153.60   $153.60  
  Purchase #4 $233.44   9.400%   $255.3834   $255.38   $255.40   $255.40  
  Purchase #5 $247.50   7.807%   $266.8223   $266.82   $266.80   $266.80  
  Purchase #6 $41.57   6.159%   $44.1303   $44.13   $44.15   $44.10  
  Purchase #7 $167.31   11.471%   $186.5021   $186.50   $186.50   $186.50  
  7 purchase totals = $1,105.93       $1,199.5945   $1,199.58   $1,199.60   $1,199.60