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 $162.75   13.547%   $184.7977   $184.80   $184.80   $184.80  
  Purchase #2 $87.75   9.772%   $96.3249   $96.32   $96.30   $96.30  
  Purchase #3 $143.54   7.692%   $154.5811   $154.58   $154.60   $154.60  
  Purchase #4 $51.37   13.415%   $58.2613   $58.26   $58.25   $58.30  
  Purchase #5 $163.69   12.763%   $184.5818   $184.58   $184.60   $184.60  
  Purchase #6 $118.60   10.459%   $131.0044   $131.00   $131.00   $131.00  
  Purchase #7 $6.77   8.181%   $7.3239   $7.32   $7.30   $7.30  
  7 purchase totals = $734.47       $816.8751   $816.86   $816.85   $816.90