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 $181.70   6.207%   $192.9781   $192.98   $193.00   $193.00  
  Purchase #2 $55.25   9.211%   $60.3391   $60.34   $60.35   $60.30  
  Purchase #3 $236.30   4.374%   $246.6358   $246.64   $246.65   $246.60  
  Purchase #4 $155.51   8.149%   $168.1825   $168.18   $168.20   $168.20  
  Purchase #5 $222.69   6.316%   $236.7551   $236.76   $236.75   $236.80  
  Purchase #6 $171.59   12.309%   $192.711   $192.71   $192.70   $192.70  
  Purchase #7 $53.93   12.557%   $60.702   $60.70   $60.70   $60.70  
  7 purchase totals = $1,076.97       $1,158.3036   $1,158.31   $1,158.35   $1,158.30