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 $151.43   8.707%   $164.615   $164.62   $164.60   $164.60  
  Purchase #2 $175.41   11.326%   $195.2769   $195.28   $195.30   $195.30  
  Purchase #3 $63.61   8.580%   $69.0677   $69.07   $69.05   $69.10  
  Purchase #4 $204.67   12.613%   $230.485   $230.49   $230.50   $230.50  
  Purchase #5 $57.48   7.202%   $61.6197   $61.62   $61.60   $61.60  
  Purchase #6 $68.94   12.653%   $77.663   $77.66   $77.65   $77.70  
  Purchase #7 $190.44   3.352%   $196.8235   $196.82   $196.80   $196.80  
  7 purchase totals = $911.98       $995.5508   $995.56   $995.50   $995.60