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 $247.42   4.682%   $259.0042   $259.00   $259.00   $259.00  
  Purchase #2 $190.28   11.607%   $212.3658   $212.37   $212.35   $212.40  
  Purchase #3 $27.34   3.192%   $28.2127   $28.21   $28.20   $28.20  
  Purchase #4 $63.91   11.508%   $71.2648   $71.26   $71.25   $71.30  
  Purchase #5 $153.76   8.586%   $166.9618   $166.96   $166.95   $167.00  
  Purchase #6 $156.33   11.534%   $174.3611   $174.36   $174.35   $174.40  
  Purchase #7 $207.88   3.319%   $214.7795   $214.78   $214.80   $214.80  
  7 purchase totals = $1,046.92       $1,126.9499   $1,126.94   $1,126.90   $1,127.10