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 $196.98   7.621%   $211.9918   $211.99   $212.00   $212.00  
  Purchase #2 $80.57   12.649%   $90.7613   $90.76   $90.75   $90.80  
  Purchase #3 $60.82   8.475%   $65.9745   $65.97   $65.95   $66.00  
  Purchase #4 $71.87   12.240%   $80.6669   $80.67   $80.65   $80.70  
  Purchase #5 $22.44   7.861%   $24.204   $24.20   $24.20   $24.20  
  Purchase #6 $149.43   5.538%   $157.7054   $157.71   $157.70   $157.70  
  Purchase #7 $191.27   7.558%   $205.7262   $205.73   $205.75   $205.70  
  7 purchase totals = $773.38       $837.0301   $837.03   $837.00   $837.10