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 $53.36   12.559%   $60.0615   $60.06   $60.05   $60.10  
  Purchase #2 $202.44   10.327%   $223.346   $223.35   $223.35   $223.30  
  Purchase #3 $88.51   8.641%   $96.1581   $96.16   $96.15   $96.20  
  Purchase #4 $211.34   13.668%   $240.226   $240.23   $240.25   $240.20  
  Purchase #5 $6.73   7.808%   $7.2555   $7.26   $7.25   $7.30  
  Purchase #6 $228.59   11.476%   $254.823   $254.82   $254.80   $254.80  
  Purchase #7 $101.73   4.127%   $105.9284   $105.93   $105.95   $105.90  
  7 purchase totals = $892.70       $987.7985   $987.81   $987.80   $987.80