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 $176.28   3.151%   $181.8346   $181.83   $181.85   $181.80  
  Purchase #2 $208.98   3.696%   $216.7039   $216.70   $216.70   $216.70  
  Purchase #3 $55.60   11.527%   $62.009   $62.01   $62.00   $62.00  
  Purchase #4 $18.53   4.484%   $19.3609   $19.36   $19.35   $19.40  
  Purchase #5 $55.54   11.570%   $61.966   $61.97   $61.95   $62.00  
  Purchase #6 $238.35   3.630%   $247.0021   $247.00   $247.00   $247.00  
  Purchase #7 $196.97   8.872%   $214.4452   $214.45   $214.45   $214.40  
  7 purchase totals = $950.25       $1,003.3217   $1,003.32   $1,003.30   $1,003.30