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 $239.27   13.529%   $271.6408   $271.64   $271.65   $271.60  
  Purchase #2 $171.57   9.194%   $187.3441   $187.34   $187.35   $187.30  
  Purchase #3 $23.96   9.112%   $26.1432   $26.14   $26.15   $26.10  
  Purchase #4 $232.98   3.551%   $241.2531   $241.25   $241.25   $241.30  
  Purchase #5 $86.95   8.167%   $94.0512   $94.05   $94.05   $94.10  
  Purchase #6 $47.31   7.391%   $50.8067   $50.81   $50.80   $50.80  
  Purchase #7 $223.38   9.825%   $245.3271   $245.33   $245.35   $245.30  
  7 purchase totals = $1,025.42       $1,116.5662   $1,116.56   $1,116.60   $1,116.50