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 $213.44   8.526%   $231.6379   $231.64   $231.65   $231.60  
  Purchase #2 $182.70   10.679%   $202.2105   $202.21   $202.20   $202.20  
  Purchase #3 $50.70   4.633%   $53.0489   $53.05   $53.05   $53.00  
  Purchase #4 $183.97   5.232%   $193.5953   $193.60   $193.60   $193.60  
  Purchase #5 $23.77   13.724%   $27.0322   $27.03   $27.05   $27.00  
  Purchase #6 $153.58   3.407%   $158.8125   $158.81   $158.80   $158.80  
  Purchase #7 $179.62   13.615%   $204.0753   $204.08   $204.10   $204.10  
  7 purchase totals = $987.78       $1,070.4126   $1,070.42   $1,070.45   $1,070.30