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 $93.69   4.703%   $98.0962   $98.10   $98.10   $98.10  
  Purchase #2 $19.99   3.195%   $20.6287   $20.63   $20.65   $20.60  
  Purchase #3 $179.29   4.781%   $187.8619   $187.86   $187.85   $187.90  
  Purchase #4 $89.35   7.394%   $95.9565   $95.96   $95.95   $96.00  
  Purchase #5 $232.71   11.245%   $258.8782   $258.88   $258.90   $258.90  
  Purchase #6 $183.88   5.391%   $193.793   $193.79   $193.80   $193.80  
  Purchase #7 $233.67   10.633%   $258.5161   $258.52   $258.50   $258.50  
  7 purchase totals = $1,032.58       $1,113.7306   $1,113.74   $1,113.75   $1,113.80