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 $62.76   11.534%   $69.9987   $70.00   $70.00   $70.00  
  Purchase #2 $39.41   9.734%   $43.2462   $43.25   $43.25   $43.20  
  Purchase #3 $162.57   8.823%   $176.9136   $176.91   $176.90   $176.90  
  Purchase #4 $191.99   9.386%   $210.0102   $210.01   $210.00   $210.00  
  Purchase #5 $92.47   9.583%   $101.3314   $101.33   $101.35   $101.30  
  Purchase #6 $203.40   13.781%   $231.4306   $231.43   $231.45   $231.40  
  Purchase #7 $248.68   4.571%   $260.0472   $260.05   $260.05   $260.00  
  7 purchase totals = $1,001.28       $1,092.9779   $1,092.98   $1,093.00   $1,092.80