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 $66.26   7.818%   $71.4402   $71.44   $71.45   $71.40  
  Purchase #2 $181.37   10.577%   $200.5535   $200.55   $200.55   $200.60  
  Purchase #3 $162.25   6.671%   $173.0737   $173.07   $173.05   $173.10  
  Purchase #4 $188.59   3.850%   $195.8507   $195.85   $195.85   $195.90  
  Purchase #5 $193.55   8.318%   $209.6495   $209.65   $209.65   $209.60  
  Purchase #6 $200.69   12.467%   $225.71   $225.71   $225.70   $225.70  
  Purchase #7 $148.48   10.164%   $163.5715   $163.57   $163.55   $163.60  
  7 purchase totals = $1,141.19       $1,239.8491   $1,239.84   $1,239.80   $1,239.90