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 $197.95   7.569%   $212.9328   $212.93   $212.95   $212.90  
  Purchase #2 $101.32   11.747%   $113.2221   $113.22   $113.20   $113.20  
  Purchase #3 $65.60   10.469%   $72.4677   $72.47   $72.45   $72.50  
  Purchase #4 $235.46   10.388%   $259.9196   $259.92   $259.90   $259.90  
  Purchase #5 $100.58   5.164%   $105.774   $105.77   $105.75   $105.80  
  Purchase #6 $88.76   7.759%   $95.6469   $95.65   $95.65   $95.60  
  Purchase #7 $198.29   3.494%   $205.2183   $205.22   $205.20   $205.20  
  7 purchase totals = $987.96       $1,065.1814   $1,065.18   $1,065.10   $1,065.10