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 $112.49   9.342%   $122.9988   $123.00   $123.00   $123.00  
  Purchase #2 $246.98   6.766%   $263.6907   $263.69   $263.70   $263.70  
  Purchase #3 $16.58   11.231%   $18.4421   $18.44   $18.45   $18.40  
  Purchase #4 $187.36   7.631%   $201.6574   $201.66   $201.65   $201.70  
  Purchase #5 $58.84   3.497%   $60.8976   $60.90   $60.90   $60.90  
  Purchase #6 $232.29   9.738%   $254.9104   $254.91   $254.90   $254.90  
  Purchase #7 $126.29   5.354%   $133.0516   $133.05   $133.05   $133.10  
  7 purchase totals = $980.83       $1,055.6486   $1,055.65   $1,055.65   $1,055.70