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 $243.88   7.646%   $262.5271   $262.53   $262.55   $262.50  
  Purchase #2 $64.53   4.705%   $67.5661   $67.57   $67.55   $67.60  
  Purchase #3 $55.80   10.192%   $61.4871   $61.49   $61.50   $61.50  
  Purchase #4 $188.89   5.118%   $198.5574   $198.56   $198.55   $198.60  
  Purchase #5 $250.51   9.232%   $273.6371   $273.64   $273.65   $273.60  
  Purchase #6 $181.93   7.539%   $195.6457   $195.65   $195.65   $195.60  
  Purchase #7 $8.63   8.394%   $9.3544   $9.35   $9.35   $9.40  
  7 purchase totals = $994.17       $1,068.7749   $1,068.79   $1,068.80   $1,068.80