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 $128.70   10.113%   $141.7154   $141.72   $141.70   $141.70  
  Purchase #2 $203.43   11.518%   $226.8611   $226.86   $226.85   $226.90  
  Purchase #3 $237.68   11.309%   $264.5592   $264.56   $264.55   $264.60  
  Purchase #4 $100.85   5.579%   $106.4764   $106.48   $106.50   $106.50  
  Purchase #5 $208.89   3.494%   $216.1886   $216.19   $216.20   $216.20  
  Purchase #6 $23.94   11.489%   $26.6905   $26.69   $26.70   $26.70  
  Purchase #7 $80.54   5.503%   $84.9721   $84.97   $84.95   $85.00  
  7 purchase totals = $984.03       $1,067.4633   $1,067.47   $1,067.45   $1,067.60