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 $232.63   5.444%   $245.2944   $245.29   $245.30   $245.30  
  Purchase #2 $177.82   4.631%   $186.0548   $186.05   $186.05   $186.10  
  Purchase #3 $194.31   5.270%   $204.5501   $204.55   $204.55   $204.60  
  Purchase #4 $108.31   5.821%   $114.6147   $114.61   $114.60   $114.60  
  Purchase #5 $98.98   5.433%   $104.3576   $104.36   $104.35   $104.40  
  Purchase #6 $159.81   9.253%   $174.5972   $174.60   $174.60   $174.60  
  Purchase #7 $179.35   13.248%   $203.1103   $203.11   $203.10   $203.10  
  7 purchase totals = $1,151.21       $1,232.5791   $1,232.57   $1,232.55   $1,232.70