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 $50.57   4.732%   $52.963   $52.96   $52.95   $53.00  
  Purchase #2 $83.49   11.832%   $93.3685   $93.37   $93.35   $93.40  
  Purchase #3 $210.93   9.643%   $231.27   $231.27   $231.25   $231.30  
  Purchase #4 $250.61   9.170%   $273.5909   $273.59   $273.60   $273.60  
  Purchase #5 $168.64   11.866%   $188.6508   $188.65   $188.65   $188.70  
  Purchase #6 $39.77   12.152%   $44.6029   $44.60   $44.60   $44.60  
  Purchase #7 $188.53   9.783%   $206.9739   $206.97   $206.95   $207.00  
  7 purchase totals = $992.54       $1,091.4200   $1,091.41   $1,091.35   $1,091.60