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 $61.92   12.566%   $69.7009   $69.70   $69.70   $69.70  
  Purchase #2 $140.72   6.168%   $149.3996   $149.40   $149.40   $149.40  
  Purchase #3 $177.29   6.678%   $189.1294   $189.13   $189.15   $189.10  
  Purchase #4 $227.89   6.510%   $242.7256   $242.73   $242.75   $242.70  
  Purchase #5 $44.28   8.279%   $47.9459   $47.95   $47.95   $47.90  
  Purchase #6 $161.74   13.369%   $183.363   $183.36   $183.35   $183.40  
  Purchase #7 $8.78   8.844%   $9.5565   $9.56   $9.55   $9.60  
  7 purchase totals = $822.62       $891.8209   $891.83   $891.85   $891.80