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 $83.96   9.543%   $91.9723   $91.97   $91.95   $92.00  
  Purchase #2 $60.35   4.714%   $63.1949   $63.19   $63.20   $63.20  
  Purchase #3 $174.27   7.122%   $186.6815   $186.68   $186.70   $186.70  
  Purchase #4 $184.90   6.842%   $197.5509   $197.55   $197.55   $197.60  
  Purchase #5 $34.33   8.846%   $37.3668   $37.37   $37.35   $37.40  
  Purchase #6 $19.80   11.778%   $22.132   $22.13   $22.15   $22.10  
  Purchase #7 $70.73   11.141%   $78.61   $78.61   $78.60   $78.60  
  7 purchase totals = $628.34       $677.5084   $677.50   $677.50   $677.60