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 $34.88   3.260%   $36.0171   $36.02   $36.00   $36.00  
  Purchase #2 $248.68   6.549%   $264.9661   $264.97   $264.95   $265.00  
  Purchase #3 $232.63   5.333%   $245.0362   $245.04   $245.05   $245.00  
  Purchase #4 $162.79   8.667%   $176.899   $176.90   $176.90   $176.90  
  Purchase #5 $223.91   13.821%   $254.8566   $254.86   $254.85   $254.90  
  Purchase #6 $82.55   6.329%   $87.7746   $87.77   $87.75   $87.80  
  Purchase #7 $81.45   12.617%   $91.7265   $91.73   $91.75   $91.70  
  7 purchase totals = $1,066.89       $1,157.2761   $1,157.29   $1,157.25   $1,157.30