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 $161.65   10.534%   $178.6782   $178.68   $178.70   $178.70  
  Purchase #2 $95.33   8.605%   $103.5331   $103.53   $103.55   $103.50  
  Purchase #3 $108.34   9.713%   $118.8631   $118.86   $118.85   $118.90  
  Purchase #4 $74.68   12.834%   $84.2644   $84.26   $84.25   $84.30  
  Purchase #5 $12.51   6.379%   $13.308   $13.31   $13.30   $13.30  
  Purchase #6 $37.41   5.505%   $39.4694   $39.47   $39.45   $39.50  
  Purchase #7 $204.77   10.385%   $226.0354   $226.04   $226.05   $226.00  
  7 purchase totals = $694.69       $764.1516   $764.15   $764.15   $764.20