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 $93.75   9.336%   $102.5025   $102.50   $102.50   $102.50  
  Purchase #2 $250.42   6.753%   $267.3309   $267.33   $267.35   $267.30  
  Purchase #3 $64.27   5.449%   $67.7721   $67.77   $67.75   $67.80  
  Purchase #4 $192.90   11.433%   $214.9543   $214.95   $214.95   $215.00  
  Purchase #5 $26.41   3.208%   $27.2572   $27.26   $27.25   $27.30  
  Purchase #6 $248.94   11.865%   $278.4767   $278.48   $278.50   $278.50  
  Purchase #7 $49.97   5.372%   $52.6544   $52.65   $52.65   $52.70  
  7 purchase totals = $926.66       $1,010.9481   $1,010.94   $1,010.95   $1,011.10