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 $188.87   6.869%   $201.8435   $201.84   $201.85   $201.80  
  Purchase #2 $239.80   6.530%   $255.4589   $255.46   $255.45   $255.50  
  Purchase #3 $235.29   4.253%   $245.2969   $245.30   $245.30   $245.30  
  Purchase #4 $52.52   9.358%   $57.4348   $57.43   $57.45   $57.40  
  Purchase #5 $191.40   11.343%   $213.1105   $213.11   $213.10   $213.10  
  Purchase #6 $240.52   10.393%   $265.5172   $265.52   $265.50   $265.50  
  Purchase #7 $28.64   3.247%   $29.5699   $29.57   $29.55   $29.60  
  7 purchase totals = $1,177.04       $1,268.2317   $1,268.23   $1,268.20   $1,268.20