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 $52.51   6.594%   $55.9725   $55.97   $55.95   $56.00  
  Purchase #2 $101.35   5.279%   $106.7003   $106.70   $106.70   $106.70  
  Purchase #3 $33.31   5.765%   $35.2303   $35.23   $35.25   $35.20  
  Purchase #4 $63.57   9.704%   $69.7388   $69.74   $69.75   $69.70  
  Purchase #5 $130.42   11.214%   $145.0453   $145.05   $145.05   $145.00  
  Purchase #6 $174.44   12.186%   $195.6973   $195.70   $195.70   $195.70  
  Purchase #7 $222.93   13.767%   $253.6208   $253.62   $253.60   $253.60  
  7 purchase totals = $778.53       $862.0053   $862.01   $862.00   $861.90