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 $61.76   8.865%   $67.235   $67.24   $67.25   $67.20  
  Purchase #2 $233.81   13.289%   $264.881   $264.88   $264.90   $264.90  
  Purchase #3 $38.77   11.570%   $43.2557   $43.26   $43.25   $43.30  
  Purchase #4 $84.75   12.316%   $95.1878   $95.19   $95.20   $95.20  
  Purchase #5 $204.66   6.432%   $217.8237   $217.82   $217.80   $217.80  
  Purchase #6 $34.45   8.634%   $37.4244   $37.42   $37.40   $37.40  
  Purchase #7 $250.92   9.524%   $274.8176   $274.82   $274.80   $274.80  
  7 purchase totals = $909.12       $1,000.6252   $1,000.63   $1,000.60   $1,000.60