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 $236.29   13.227%   $267.5441   $267.54   $267.55   $267.50  
  Purchase #2 $193.94   8.789%   $210.9854   $210.99   $211.00   $211.00  
  Purchase #3 $54.99   13.794%   $62.5753   $62.58   $62.60   $62.60  
  Purchase #4 $239.50   12.454%   $269.3273   $269.33   $269.35   $269.30  
  Purchase #5 $122.75   7.407%   $131.8421   $131.84   $131.85   $131.80  
  Purchase #6 $92.35   6.675%   $98.5144   $98.51   $98.50   $98.50  
  Purchase #7 $21.75   9.153%   $23.7408   $23.74   $23.75   $23.70  
  7 purchase totals = $961.57       $1,064.5294   $1,064.53   $1,064.60   $1,064.40