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 $182.87   13.107%   $206.8388   $206.84   $206.85   $206.80  
  Purchase #2 $222.62   11.240%   $247.6425   $247.64   $247.65   $247.60  
  Purchase #3 $159.40   8.256%   $172.5601   $172.56   $172.55   $172.60  
  Purchase #4 $97.98   9.413%   $107.2029   $107.20   $107.20   $107.20  
  Purchase #5 $172.32   6.835%   $184.0981   $184.10   $184.10   $184.10  
  Purchase #6 $224.70   3.626%   $232.8476   $232.85   $232.85   $232.80  
  Purchase #7 $47.63   9.325%   $52.0715   $52.07   $52.05   $52.10  
  7 purchase totals = $1,107.52       $1,203.2615   $1,203.26   $1,203.25   $1,203.20