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 $91.56   4.257%   $95.4577   $95.46   $95.45   $95.50  
  Purchase #2 $147.27   12.263%   $165.3297   $165.33   $165.35   $165.30  
  Purchase #3 $64.90   8.765%   $70.5885   $70.59   $70.60   $70.60  
  Purchase #4 $207.46   5.225%   $218.2998   $218.30   $218.30   $218.30  
  Purchase #5 $20.56   13.119%   $23.2573   $23.26   $23.25   $23.30  
  Purchase #6 $45.51   9.529%   $49.8466   $49.85   $49.85   $49.80  
  Purchase #7 $175.80   9.526%   $192.5467   $192.55   $192.55   $192.50  
  7 purchase totals = $753.06       $815.3263   $815.34   $815.35   $815.30