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 $173.79   12.823%   $196.0751   $196.08   $196.10   $196.10  
  Purchase #2 $109.40   13.578%   $124.2543   $124.25   $124.25   $124.30  
  Purchase #3 $112.33   11.594%   $125.3535   $125.35   $125.35   $125.40  
  Purchase #4 $241.40   8.325%   $261.4966   $261.50   $261.50   $261.50  
  Purchase #5 $35.26   4.709%   $36.9204   $36.92   $36.90   $36.90  
  Purchase #6 $201.30   7.789%   $216.9793   $216.98   $217.00   $217.00  
  Purchase #7 $147.63   13.581%   $167.6796   $167.68   $167.70   $167.70  
  7 purchase totals = $1,021.11       $1,128.7588   $1,128.76   $1,128.80   $1,128.90