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 $250.73   12.834%   $282.9087   $282.91   $282.90   $282.90  
  Purchase #2 $178.35   12.770%   $201.1253   $201.13   $201.15   $201.10  
  Purchase #3 $178.57   13.222%   $202.1805   $202.18   $202.20   $202.20  
  Purchase #4 $38.31   13.597%   $43.519   $43.52   $43.50   $43.50  
  Purchase #5 $32.70   13.829%   $37.2221   $37.22   $37.20   $37.20  
  Purchase #6 $222.65   5.376%   $234.6197   $234.62   $234.60   $234.60  
  Purchase #7 $176.87   13.685%   $201.0747   $201.07   $201.05   $201.10  
  7 purchase totals = $1,078.18       $1,202.6500   $1,202.65   $1,202.60   $1,202.60