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 $108.45   4.755%   $113.6068   $113.61   $113.60   $113.60  
  Purchase #2 $161.94   12.793%   $182.657   $182.66   $182.65   $182.70  
  Purchase #3 $247.47   8.525%   $268.5668   $268.57   $268.55   $268.60  
  Purchase #4 $171.77   12.522%   $193.279   $193.28   $193.30   $193.30  
  Purchase #5 $85.37   12.678%   $96.1932   $96.19   $96.20   $96.20  
  Purchase #6 $128.55   7.740%   $138.4998   $138.50   $138.50   $138.50  
  Purchase #7 $31.53   5.697%   $33.3263   $33.33   $33.35   $33.30  
  7 purchase totals = $935.08       $1,026.1289   $1,026.14   $1,026.15   $1,026.20