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 $86.85   5.112%   $91.2898   $91.29   $91.30   $91.30  
  Purchase #2 $208.31   13.135%   $235.6715   $235.67   $235.65   $235.70  
  Purchase #3 $32.35   8.418%   $35.0732   $35.07   $35.05   $35.10  
  Purchase #4 $177.97   3.295%   $183.8341   $183.83   $183.85   $183.80  
  Purchase #5 $192.71   5.631%   $203.5615   $203.56   $203.55   $203.60  
  Purchase #6 $216.97   6.765%   $231.648   $231.65   $231.65   $231.60  
  Purchase #7 $57.47   5.745%   $60.7717   $60.77   $60.75   $60.80  
  7 purchase totals = $972.63       $1,041.8498   $1,041.84   $1,041.80   $1,041.90