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 $98.58   3.422%   $101.9534   $101.95   $101.95   $102.00  
  Purchase #2 $223.88   7.297%   $240.2165   $240.22   $240.20   $240.20  
  Purchase #3 $245.37   5.129%   $257.955   $257.96   $257.95   $258.00  
  Purchase #4 $31.52   10.589%   $34.8577   $34.86   $34.85   $34.90  
  Purchase #5 $120.47   3.526%   $124.7178   $124.72   $124.70   $124.70  
  Purchase #6 $54.26   10.671%   $60.0501   $60.05   $60.05   $60.10  
  Purchase #7 $221.67   13.509%   $251.6154   $251.62   $251.60   $251.60  
  7 purchase totals = $995.75       $1,071.3659   $1,071.38   $1,071.30   $1,071.50