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 $216.96   3.744%   $225.083   $225.08   $225.10   $225.10  
  Purchase #2 $43.97   9.438%   $48.1199   $48.12   $48.10   $48.10  
  Purchase #3 $54.99   4.568%   $57.5019   $57.50   $57.50   $57.50  
  Purchase #4 $249.81   12.567%   $281.2036   $281.20   $281.20   $281.20  
  Purchase #5 $48.48   7.708%   $52.2168   $52.22   $52.20   $52.20  
  Purchase #6 $180.47   7.763%   $194.4799   $194.48   $194.50   $194.50  
  Purchase #7 $151.88   8.439%   $164.6972   $164.70   $164.70   $164.70  
  7 purchase totals = $946.56       $1,023.3023   $1,023.30   $1,023.30   $1,023.30