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 $96.97   4.110%   $100.9555   $100.96   $100.95   $101.00  
  Purchase #2 $156.46   13.561%   $177.6775   $177.68   $177.70   $177.70  
  Purchase #3 $174.35   7.640%   $187.6703   $187.67   $187.65   $187.70  
  Purchase #4 $58.89   9.173%   $64.292   $64.29   $64.30   $64.30  
  Purchase #5 $241.65   10.209%   $266.32   $266.32   $266.30   $266.30  
  Purchase #6 $158.73   6.149%   $168.4903   $168.49   $168.50   $168.50  
  Purchase #7 $10.35   7.430%   $11.119   $11.12   $11.10   $11.10  
  7 purchase totals = $897.40       $976.5246   $976.53   $976.50   $976.60