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 $168.31   7.541%   $181.0023   $181.00   $181.00   $181.00  
  Purchase #2 $179.54   3.569%   $185.9478   $185.95   $185.95   $185.90  
  Purchase #3 $60.35   8.303%   $65.3609   $65.36   $65.35   $65.40  
  Purchase #4 $227.78   10.524%   $251.7516   $251.75   $251.75   $251.80  
  Purchase #5 $211.42   11.353%   $235.4225   $235.42   $235.40   $235.40  
  Purchase #6 $31.90   8.738%   $34.6874   $34.69   $34.70   $34.70  
  Purchase #7 $125.57   9.277%   $137.2191   $137.22   $137.20   $137.20  
  7 purchase totals = $1,004.87       $1,091.3916   $1,091.39   $1,091.35   $1,091.40