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 $240.79   9.201%   $262.9451   $262.95   $262.95   $262.90  
  Purchase #2 $184.68   7.623%   $198.7582   $198.76   $198.75   $198.80  
  Purchase #3 $237.27   12.788%   $267.6121   $267.61   $267.60   $267.60  
  Purchase #4 $86.97   11.233%   $96.7393   $96.74   $96.75   $96.70  
  Purchase #5 $33.45   4.145%   $34.8365   $34.84   $34.85   $34.80  
  Purchase #6 $94.97   13.225%   $107.5298   $107.53   $107.55   $107.50  
  Purchase #7 $70.98   9.203%   $77.5123   $77.51   $77.50   $77.50  
  7 purchase totals = $949.11       $1,045.9333   $1,045.94   $1,045.95   $1,045.80