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 $22.38   13.482%   $25.3973   $25.40   $25.40   $25.40  
  Purchase #2 $220.61   10.536%   $243.8535   $243.85   $243.85   $243.90  
  Purchase #3 $134.42   9.747%   $147.5219   $147.52   $147.50   $147.50  
  Purchase #4 $15.46   9.130%   $16.8715   $16.87   $16.85   $16.90  
  Purchase #5 $152.52   10.624%   $168.7237   $168.72   $168.70   $168.70  
  Purchase #6 $214.62   8.259%   $232.3455   $232.35   $232.35   $232.30  
  Purchase #7 $180.72   4.835%   $189.4578   $189.46   $189.45   $189.50  
  7 purchase totals = $940.73       $1,024.1712   $1,024.17   $1,024.10   $1,024.20