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 $116.51   5.229%   $122.6023   $122.60   $122.60   $122.60  
  Purchase #2 $218.33   8.299%   $236.4492   $236.45   $236.45   $236.40  
  Purchase #3 $219.87   6.503%   $234.1681   $234.17   $234.15   $234.20  
  Purchase #4 $54.27   8.832%   $59.0631   $59.06   $59.05   $59.10  
  Purchase #5 $246.55   4.846%   $258.4978   $258.50   $258.50   $258.50  
  Purchase #6 $221.65   10.470%   $244.8568   $244.86   $244.85   $244.90  
  Purchase #7 $30.70   10.501%   $33.9238   $33.92   $33.90   $33.90  
  7 purchase totals = $1,107.88       $1,189.5611   $1,189.56   $1,189.50   $1,189.60