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 $163.49   10.270%   $180.2804   $180.28   $180.30   $180.30  
  Purchase #2 $185.32   7.572%   $199.3524   $199.35   $199.35   $199.40  
  Purchase #3 $207.27   10.292%   $228.6022   $228.60   $228.60   $228.60  
  Purchase #4 $23.98   3.602%   $24.8438   $24.84   $24.85   $24.80  
  Purchase #5 $80.61   6.529%   $85.873   $85.87   $85.85   $85.90  
  Purchase #6 $95.75   5.418%   $100.9377   $100.94   $100.95   $100.90  
  Purchase #7 $49.67   13.263%   $56.2577   $56.26   $56.25   $56.30  
  7 purchase totals = $806.09       $876.1472   $876.14   $876.15   $876.20