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 $86.78   6.780%   $92.6637   $92.66   $92.65   $92.70  
  Purchase #2 $226.52   10.244%   $249.7247   $249.72   $249.70   $249.70  
  Purchase #3 $94.41   6.648%   $100.6864   $100.69   $100.70   $100.70  
  Purchase #4 $197.37   11.590%   $220.2452   $220.25   $220.25   $220.20  
  Purchase #5 $95.77   5.671%   $101.2011   $101.20   $101.20   $101.20  
  Purchase #6 $44.85   6.521%   $47.7747   $47.77   $47.75   $47.80  
  Purchase #7 $224.65   9.106%   $245.1066   $245.11   $245.10   $245.10  
  7 purchase totals = $970.35       $1,057.4024   $1,057.40   $1,057.35   $1,057.40