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 $123.76   13.136%   $140.0171   $140.02   $140.00   $140.00  
  Purchase #2 $96.27   11.109%   $106.9646   $106.96   $106.95   $107.00  
  Purchase #3 $58.89   10.186%   $64.8885   $64.89   $64.90   $64.90  
  Purchase #4 $87.29   3.862%   $90.6611   $90.66   $90.65   $90.70  
  Purchase #5 $35.29   5.436%   $37.2084   $37.21   $37.20   $37.20  
  Purchase #6 $161.25   7.281%   $172.9906   $172.99   $173.00   $173.00  
  Purchase #7 $138.45   11.764%   $154.7373   $154.74   $154.75   $154.70  
  7 purchase totals = $701.20       $767.4676   $767.47   $767.45   $767.50