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 $189.38   8.152%   $204.8183   $204.82   $204.80   $204.80  
  Purchase #2 $173.41   7.695%   $186.7539   $186.75   $186.75   $186.80  
  Purchase #3 $48.77   8.162%   $52.7506   $52.75   $52.75   $52.80  
  Purchase #4 $191.93   13.351%   $217.5546   $217.55   $217.55   $217.60  
  Purchase #5 $7.59   8.332%   $8.2224   $8.22   $8.20   $8.20  
  Purchase #6 $242.79   8.571%   $263.5995   $263.60   $263.60   $263.60  
  Purchase #7 $161.56   10.237%   $178.0989   $178.10   $178.10   $178.10  
  7 purchase totals = $1,015.43       $1,111.7982   $1,111.79   $1,111.75   $1,111.90