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 $56.84   11.158%   $63.1822   $63.18   $63.20   $63.20  
  Purchase #2 $204.82   9.486%   $224.2492   $224.25   $224.25   $224.20  
  Purchase #3 $241.94   11.282%   $269.2357   $269.24   $269.25   $269.20  
  Purchase #4 $136.36   8.640%   $148.1415   $148.14   $148.15   $148.10  
  Purchase #5 $49.77   3.829%   $51.6757   $51.68   $51.70   $51.70  
  Purchase #6 $110.92   12.601%   $124.897   $124.90   $124.90   $124.90  
  Purchase #7 $118.46   12.512%   $133.2817   $133.28   $133.30   $133.30  
  7 purchase totals = $919.11       $1,014.6630   $1,014.67   $1,014.75   $1,014.60