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 $226.82   8.414%   $245.9046   $245.90   $245.90   $245.90  
  Purchase #2 $176.32   12.422%   $198.2225   $198.22   $198.20   $198.20  
  Purchase #3 $111.64   13.124%   $126.2916   $126.29   $126.30   $126.30  
  Purchase #4 $33.36   4.791%   $34.9583   $34.96   $34.95   $35.00  
  Purchase #5 $77.86   3.141%   $80.3056   $80.31   $80.30   $80.30  
  Purchase #6 $187.78   6.807%   $200.5622   $200.56   $200.55   $200.60  
  Purchase #7 $122.51   4.830%   $128.4272   $128.43   $128.45   $128.40  
  7 purchase totals = $936.29       $1,014.6720   $1,014.67   $1,014.65   $1,014.70