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 $92.37   6.619%   $98.484   $98.48   $98.50   $98.50  
  Purchase #2 $84.81   8.139%   $91.7127   $91.71   $91.70   $91.70  
  Purchase #3 $196.68   12.366%   $221.0014   $221.00   $221.00   $221.00  
  Purchase #4 $112.87   6.704%   $120.4368   $120.44   $120.45   $120.40  
  Purchase #5 $229.27   4.240%   $238.991   $238.99   $239.00   $239.00  
  Purchase #6 $91.51   4.380%   $95.5181   $95.52   $95.50   $95.50  
  Purchase #7 $141.40   9.761%   $155.2021   $155.20   $155.20   $155.20  
  7 purchase totals = $948.91       $1,021.3461   $1,021.34   $1,021.35   $1,021.30