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 $76.32   10.665%   $84.4595   $84.46   $84.45   $84.50  
  Purchase #2 $99.61   4.235%   $103.8285   $103.83   $103.85   $103.80  
  Purchase #3 $99.65   11.343%   $110.9533   $110.95   $110.95   $111.00  
  Purchase #4 $156.42   7.147%   $167.5993   $167.60   $167.60   $167.60  
  Purchase #5 $137.98   4.287%   $143.8952   $143.90   $143.90   $143.90  
  Purchase #6 $200.32   5.682%   $211.7022   $211.70   $211.70   $211.70  
  Purchase #7 $224.45   5.507%   $236.8105   $236.81   $236.80   $236.80  
  7 purchase totals = $994.75       $1,059.2485   $1,059.25   $1,059.25   $1,059.30