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 $217.67   11.663%   $243.0569   $243.06   $243.05   $243.10  
  Purchase #2 $68.55   8.272%   $74.2205   $74.22   $74.20   $74.20  
  Purchase #3 $115.89   4.155%   $120.7052   $120.71   $120.70   $120.70  
  Purchase #4 $162.92   11.349%   $181.4098   $181.41   $181.40   $181.40  
  Purchase #5 $182.58   6.266%   $194.0205   $194.02   $194.00   $194.00  
  Purchase #6 $223.74   6.508%   $238.301   $238.30   $238.30   $238.30  
  Purchase #7 $74.75   9.114%   $81.5627   $81.56   $81.55   $81.60  
  7 purchase totals = $1,046.10       $1,133.2766   $1,133.28   $1,133.20   $1,133.30