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 $60.28   13.256%   $68.2707   $68.27   $68.25   $68.30  
  Purchase #2 $229.38   12.841%   $258.8347   $258.83   $258.85   $258.80  
  Purchase #3 $204.37   7.810%   $220.3313   $220.33   $220.35   $220.30  
  Purchase #4 $31.71   7.601%   $34.1203   $34.12   $34.10   $34.10  
  Purchase #5 $70.94   4.657%   $74.2437   $74.24   $74.25   $74.20  
  Purchase #6 $204.75   6.529%   $218.1181   $218.12   $218.10   $218.10  
  Purchase #7 $106.96   13.555%   $121.4584   $121.46   $121.45   $121.50  
  7 purchase totals = $908.39       $995.3772   $995.37   $995.35   $995.30