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 $61.37   4.377%   $64.0562   $64.06   $64.05   $64.10  
  Purchase #2 $30.65   3.128%   $31.6087   $31.61   $31.60   $31.60  
  Purchase #3 $167.54   4.112%   $174.4292   $174.43   $174.45   $174.40  
  Purchase #4 $30.31   6.223%   $32.1962   $32.20   $32.20   $32.20  
  Purchase #5 $161.61   13.867%   $184.0205   $184.02   $184.00   $184.00  
  Purchase #6 $225.40   12.713%   $254.0551   $254.06   $254.05   $254.10  
  Purchase #7 $64.39   4.367%   $67.2019   $67.20   $67.20   $67.20  
  7 purchase totals = $741.27       $807.5678   $807.58   $807.55   $807.60