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 $161.60   13.604%   $183.5841   $183.58   $183.60   $183.60  
  Purchase #2 $53.86   13.291%   $61.0185   $61.02   $61.00   $61.00  
  Purchase #3 $56.85   5.583%   $60.0239   $60.02   $60.00   $60.00  
  Purchase #4 $62.51   11.702%   $69.8249   $69.82   $69.80   $69.80  
  Purchase #5 $200.33   3.418%   $207.1773   $207.18   $207.20   $207.20  
  Purchase #6 $105.53   3.401%   $109.1191   $109.12   $109.10   $109.10  
  Purchase #7 $165.32   10.529%   $182.7265   $182.73   $182.75   $182.70  
  7 purchase totals = $806.00       $873.4743   $873.47   $873.45   $873.40