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 $172.69   3.168%   $178.1608   $178.16   $178.15   $178.20  
  Purchase #2 $163.87   10.216%   $180.611   $180.61   $180.60   $180.60  
  Purchase #3 $135.48   11.354%   $150.8624   $150.86   $150.85   $150.90  
  Purchase #4 $7.60   7.479%   $8.1684   $8.17   $8.15   $8.20  
  Purchase #5 $185.62   9.397%   $203.0627   $203.06   $203.05   $203.10  
  Purchase #6 $38.91   5.647%   $41.1072   $41.11   $41.10   $41.10  
  Purchase #7 $167.55   8.349%   $181.5387   $181.54   $181.55   $181.50  
  7 purchase totals = $871.72       $943.5112   $943.51   $943.45   $943.60