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 $23.49   8.683%   $25.5296   $25.53   $25.55   $25.50  
  Purchase #2 $166.75   7.116%   $178.6159   $178.62   $178.60   $178.60  
  Purchase #3 $235.36   9.119%   $256.8225   $256.82   $256.80   $256.80  
  Purchase #4 $108.55   7.668%   $116.8736   $116.87   $116.85   $116.90  
  Purchase #5 $31.85   3.805%   $33.0619   $33.06   $33.05   $33.10  
  Purchase #6 $236.35   9.245%   $258.2006   $258.20   $258.20   $258.20  
  Purchase #7 $141.26   4.117%   $147.0757   $147.08   $147.10   $147.10  
  7 purchase totals = $943.61       $1,016.1798   $1,016.18   $1,016.15   $1,016.20