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 $68.57   7.468%   $73.6908   $73.69   $73.70   $73.70  
  Purchase #2 $164.65   8.371%   $178.4329   $178.43   $178.45   $178.40  
  Purchase #3 $241.82   9.458%   $264.6913   $264.69   $264.70   $264.70  
  Purchase #4 $108.68   9.237%   $118.7188   $118.72   $118.70   $118.70  
  Purchase #5 $164.37   3.587%   $170.266   $170.27   $170.25   $170.30  
  Purchase #6 $30.76   10.575%   $34.0129   $34.01   $34.00   $34.00  
  Purchase #7 $167.81   3.558%   $173.7807   $173.78   $173.80   $173.80  
  7 purchase totals = $946.66       $1,013.5934   $1,013.59   $1,013.60   $1,013.60