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 $56.95   6.372%   $60.5789   $60.58   $60.60   $60.60  
  Purchase #2 $27.70   3.752%   $28.7393   $28.74   $28.75   $28.70  
  Purchase #3 $157.72   10.275%   $173.9257   $173.93   $173.95   $173.90  
  Purchase #4 $101.29   10.759%   $112.1878   $112.19   $112.20   $112.20  
  Purchase #5 $178.59   8.539%   $193.8398   $193.84   $193.85   $193.80  
  Purchase #6 $115.65   10.753%   $128.0858   $128.09   $128.10   $128.10  
  Purchase #7 $97.89   3.810%   $101.6196   $101.62   $101.60   $101.60  
  7 purchase totals = $735.79       $798.9769   $798.99   $799.05   $798.90