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 $182.86   10.862%   $202.7223   $202.72   $202.70   $202.70  
  Purchase #2 $121.51   13.133%   $137.4679   $137.47   $137.45   $137.50  
  Purchase #3 $152.28   5.653%   $160.8884   $160.89   $160.90   $160.90  
  Purchase #4 $216.27   11.603%   $241.3638   $241.36   $241.35   $241.40  
  Purchase #5 $223.72   8.870%   $243.564   $243.56   $243.55   $243.60  
  Purchase #6 $248.43   11.395%   $276.7386   $276.74   $276.75   $276.70  
  Purchase #7 $88.53   10.219%   $97.5769   $97.58   $97.60   $97.60  
  7 purchase totals = $1,233.60       $1,360.3219   $1,360.32   $1,360.30   $1,360.40