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 $60.40   12.764%   $68.1095   $68.11   $68.10   $68.10  
  Purchase #2 $232.55   11.187%   $258.5654   $258.57   $258.55   $258.60  
  Purchase #3 $40.61   11.815%   $45.4081   $45.41   $45.40   $45.40  
  Purchase #4 $81.78   9.509%   $89.5565   $89.56   $89.55   $89.60  
  Purchase #5 $61.42   5.346%   $64.7035   $64.70   $64.70   $64.70  
  Purchase #6 $216.98   13.350%   $245.9468   $245.95   $245.95   $245.90  
  Purchase #7 $88.55   5.867%   $93.7452   $93.75   $93.75   $93.70  
  7 purchase totals = $782.29       $866.0350   $866.05   $866.00   $866.00