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 $172.89   8.522%   $187.6237   $187.62   $187.60   $187.60  
  Purchase #2 $226.77   11.420%   $252.6671   $252.67   $252.65   $252.70  
  Purchase #3 $193.79   11.827%   $216.7095   $216.71   $216.70   $216.70  
  Purchase #4 $65.35   9.343%   $71.4557   $71.46   $71.45   $71.50  
  Purchase #5 $117.35   8.198%   $126.9704   $126.97   $126.95   $127.00  
  Purchase #6 $144.89   5.240%   $152.4822   $152.48   $152.50   $152.50  
  Purchase #7 $39.64   11.168%   $44.067   $44.07   $44.05   $44.10  
  7 purchase totals = $960.68       $1,051.9756   $1,051.98   $1,051.90   $1,052.10