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 $124.81   7.103%   $133.6753   $133.68   $133.70   $133.70  
  Purchase #2 $85.79   6.577%   $91.4324   $91.43   $91.45   $91.40  
  Purchase #3 $70.62   6.576%   $75.264   $75.26   $75.25   $75.30  
  Purchase #4 $175.93   4.426%   $183.7167   $183.72   $183.70   $183.70  
  Purchase #5 $123.91   8.808%   $134.824   $134.82   $134.80   $134.80  
  Purchase #6 $54.45   4.764%   $57.044   $57.04   $57.05   $57.00  
  Purchase #7 $50.57   11.663%   $56.468   $56.47   $56.45   $56.50  
  7 purchase totals = $686.08       $732.4244   $732.42   $732.40   $732.40