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 $85.38   11.816%   $95.4685   $95.47   $95.45   $95.50  
  Purchase #2 $230.49   8.120%   $249.2058   $249.21   $249.20   $249.20  
  Purchase #3 $168.46   7.459%   $181.0254   $181.03   $181.05   $181.00  
  Purchase #4 $177.99   12.111%   $199.5464   $199.55   $199.55   $199.50  
  Purchase #5 $196.50   12.133%   $220.3413   $220.34   $220.35   $220.30  
  Purchase #6 $14.85   11.394%   $16.542   $16.54   $16.55   $16.50  
  Purchase #7 $8.94   3.654%   $9.2667   $9.27   $9.25   $9.30  
  7 purchase totals = $882.61       $971.3961   $971.41   $971.40   $971.30