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 $163.39   12.314%   $183.5098   $183.51   $183.50   $183.50  
  Purchase #2 $227.59   5.672%   $240.4989   $240.50   $240.50   $240.50  
  Purchase #3 $58.40   12.413%   $65.6492   $65.65   $65.65   $65.60  
  Purchase #4 $168.76   9.437%   $184.6859   $184.69   $184.70   $184.70  
  Purchase #5 $77.67   9.315%   $84.905   $84.91   $84.90   $84.90  
  Purchase #6 $180.77   3.682%   $187.426   $187.43   $187.45   $187.40  
  Purchase #7 $146.62   9.166%   $160.0592   $160.06   $160.05   $160.10  
  7 purchase totals = $1,023.20       $1,106.7340   $1,106.75   $1,106.75   $1,106.70