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 $119.88   8.618%   $130.2113   $130.21   $130.20   $130.20  
  Purchase #2 $125.61   13.581%   $142.6691   $142.67   $142.65   $142.70  
  Purchase #3 $153.57   8.506%   $166.6327   $166.63   $166.65   $166.60  
  Purchase #4 $211.53   7.437%   $227.2615   $227.26   $227.25   $227.30  
  Purchase #5 $169.69   10.204%   $187.0052   $187.01   $187.00   $187.00  
  Purchase #6 $47.39   9.807%   $52.0375   $52.04   $52.05   $52.00  
  Purchase #7 $116.96   9.457%   $128.0209   $128.02   $128.00   $128.00  
  7 purchase totals = $944.63       $1,033.8382   $1,033.84   $1,033.80   $1,033.80