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 $211.41   10.181%   $232.9337   $232.93   $232.95   $232.90  
  Purchase #2 $22.80   5.694%   $24.0982   $24.10   $24.10   $24.10  
  Purchase #3 $68.70   8.317%   $74.4138   $74.41   $74.40   $74.40  
  Purchase #4 $187.45   7.105%   $200.7683   $200.77   $200.75   $200.80  
  Purchase #5 $223.57   3.451%   $231.2854   $231.29   $231.30   $231.30  
  Purchase #6 $231.90   10.816%   $256.9823   $256.98   $257.00   $257.00  
  Purchase #7 $221.65   8.641%   $240.8028   $240.80   $240.80   $240.80  
  7 purchase totals = $1,167.48       $1,261.2845   $1,261.28   $1,261.30   $1,261.30