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 $73.56   4.553%   $76.9092   $76.91   $76.90   $76.90  
  Purchase #2 $38.53   8.388%   $41.7619   $41.76   $41.75   $41.80  
  Purchase #3 $224.34   10.536%   $247.9765   $247.98   $248.00   $248.00  
  Purchase #4 $246.50   10.615%   $272.666   $272.67   $272.65   $272.70  
  Purchase #5 $77.96   6.693%   $83.1779   $83.18   $83.20   $83.20  
  Purchase #6 $71.67   11.284%   $79.7572   $79.76   $79.75   $79.80  
  Purchase #7 $190.45   5.780%   $201.458   $201.46   $201.45   $201.50  
  7 purchase totals = $923.01       $1,003.7067   $1,003.72   $1,003.70   $1,003.90