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 $172.65   13.781%   $196.4429   $196.44   $196.45   $196.40  
  Purchase #2 $156.86   11.132%   $174.3217   $174.32   $174.30   $174.30  
  Purchase #3 $179.53   12.783%   $202.4793   $202.48   $202.50   $202.50  
  Purchase #4 $88.37   11.657%   $98.6713   $98.67   $98.65   $98.70  
  Purchase #5 $246.90   10.619%   $273.1183   $273.12   $273.10   $273.10  
  Purchase #6 $179.63   10.549%   $198.5792   $198.58   $198.60   $198.60  
  Purchase #7 $112.62   7.714%   $121.3075   $121.31   $121.30   $121.30  
  7 purchase totals = $1,136.56       $1,264.9202   $1,264.92   $1,264.90   $1,264.90