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 $207.95   8.519%   $225.6653   $225.67   $225.65   $225.70  
  Purchase #2 $188.35   8.607%   $204.5613   $204.56   $204.55   $204.60  
  Purchase #3 $35.46   4.556%   $37.0756   $37.08   $37.10   $37.10  
  Purchase #4 $56.44   13.512%   $64.0662   $64.07   $64.05   $64.10  
  Purchase #5 $149.51   9.853%   $164.2412   $164.24   $164.25   $164.20  
  Purchase #6 $241.93   12.317%   $271.7285   $271.73   $271.75   $271.70  
  Purchase #7 $78.56   7.404%   $84.3766   $84.38   $84.40   $84.40  
  7 purchase totals = $958.20       $1,051.7147   $1,051.73   $1,051.75   $1,051.80