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 $76.49   3.701%   $79.3209   $79.32   $79.30   $79.30  
  Purchase #2 $206.84   13.379%   $234.5131   $234.51   $234.50   $234.50  
  Purchase #3 $80.55   13.499%   $91.4234   $91.42   $91.40   $91.40  
  Purchase #4 $219.64   11.804%   $245.5663   $245.57   $245.55   $245.60  
  Purchase #5 $23.81   6.343%   $25.3203   $25.32   $25.30   $25.30  
  Purchase #6 $238.79   13.526%   $271.0887   $271.09   $271.10   $271.10  
  Purchase #7 $73.96   11.478%   $82.4491   $82.45   $82.45   $82.40  
  7 purchase totals = $920.08       $1,029.6818   $1,029.68   $1,029.60   $1,029.60