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 $228.27   7.613%   $245.6482   $245.65   $245.65   $245.60  
  Purchase #2 $244.35   5.672%   $258.2095   $258.21   $258.20   $258.20  
  Purchase #3 $122.86   10.309%   $135.5256   $135.53   $135.55   $135.50  
  Purchase #4 $35.55   9.737%   $39.0115   $39.01   $39.00   $39.00  
  Purchase #5 $86.65   7.361%   $93.0283   $93.03   $93.05   $93.00  
  Purchase #6 $53.91   12.425%   $60.6083   $60.61   $60.60   $60.60  
  Purchase #7 $189.41   11.426%   $211.052   $211.05   $211.05   $211.10  
  7 purchase totals = $961.00       $1,043.0834   $1,043.09   $1,043.10   $1,043.00