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 $167.52   8.161%   $181.1913   $181.19   $181.20   $181.20  
  Purchase #2 $164.96   8.482%   $178.9519   $178.95   $178.95   $179.00  
  Purchase #3 $131.36   3.144%   $135.49   $135.49   $135.50   $135.50  
  Purchase #4 $214.40   6.536%   $228.4132   $228.41   $228.40   $228.40  
  Purchase #5 $125.41   10.252%   $138.267   $138.27   $138.25   $138.30  
  Purchase #6 $179.87   12.620%   $202.5696   $202.57   $202.55   $202.60  
  Purchase #7 $182.53   5.574%   $192.7042   $192.70   $192.70   $192.70  
  7 purchase totals = $1,166.05       $1,257.5872   $1,257.58   $1,257.55   $1,257.70