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 $241.25   10.794%   $267.2905   $267.29   $267.30   $267.30  
  Purchase #2 $63.99   12.372%   $71.9068   $71.91   $71.90   $71.90  
  Purchase #3 $80.92   9.805%   $88.8542   $88.85   $88.85   $88.90  
  Purchase #4 $129.64   11.815%   $144.957   $144.96   $144.95   $145.00  
  Purchase #5 $166.49   10.201%   $183.4736   $183.47   $183.45   $183.50  
  Purchase #6 $143.28   7.233%   $153.6434   $153.64   $153.65   $153.60  
  Purchase #7 $69.64   8.233%   $75.3735   $75.37   $75.35   $75.40  
  7 purchase totals = $895.21       $985.4990   $985.49   $985.45   $985.60