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 $91.64   10.229%   $101.0139   $101.01   $101.00   $101.00  
  Purchase #2 $189.69   3.733%   $196.7711   $196.77   $196.75   $196.80  
  Purchase #3 $172.54   4.804%   $180.8288   $180.83   $180.85   $180.80  
  Purchase #4 $91.51   3.297%   $94.5271   $94.53   $94.55   $94.50  
  Purchase #5 $120.50   4.361%   $125.755   $125.76   $125.75   $125.80  
  Purchase #6 $235.89   8.219%   $255.2778   $255.28   $255.30   $255.30  
  Purchase #7 $233.41   6.315%   $248.1498   $248.15   $248.15   $248.10  
  7 purchase totals = $1,135.18       $1,202.3235   $1,202.33   $1,202.35   $1,202.30