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 $60.38   5.732%   $63.841   $63.84   $63.85   $63.80  
  Purchase #2 $230.79   3.103%   $237.9514   $237.95   $237.95   $238.00  
  Purchase #3 $58.26   9.322%   $63.691   $63.69   $63.70   $63.70  
  Purchase #4 $87.71   7.173%   $94.0014   $94.00   $94.00   $94.00  
  Purchase #5 $157.71   3.696%   $163.539   $163.54   $163.55   $163.50  
  Purchase #6 $158.25   5.600%   $167.112   $167.11   $167.10   $167.10  
  Purchase #7 $190.30   6.426%   $202.5287   $202.53   $202.55   $202.50  
  7 purchase totals = $943.40       $992.6645   $992.66   $992.70   $992.60