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 $67.28   9.334%   $73.5599   $73.56   $73.55   $73.60  
  Purchase #2 $85.92   7.180%   $92.0891   $92.09   $92.10   $92.10  
  Purchase #3 $213.42   7.860%   $230.1948   $230.19   $230.20   $230.20  
  Purchase #4 $241.99   8.719%   $263.0891   $263.09   $263.10   $263.10  
  Purchase #5 $82.34   12.752%   $92.84   $92.84   $92.85   $92.80  
  Purchase #6 $210.71   10.139%   $232.0739   $232.07   $232.05   $232.10  
  Purchase #7 $39.68   7.722%   $42.7441   $42.74   $42.75   $42.70  
  7 purchase totals = $941.34       $1,026.5909   $1,026.58   $1,026.60   $1,026.60