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 $39.26   12.171%   $44.0383   $44.04   $44.05   $44.00  
  Purchase #2 $57.85   8.363%   $62.688   $62.69   $62.70   $62.70  
  Purchase #3 $75.63   5.774%   $79.9969   $80.00   $80.00   $80.00  
  Purchase #4 $160.55   4.674%   $168.0541   $168.05   $168.05   $168.10  
  Purchase #5 $244.40   5.391%   $257.5756   $257.58   $257.60   $257.60  
  Purchase #6 $58.55   13.155%   $66.2523   $66.25   $66.25   $66.30  
  Purchase #7 $201.55   5.593%   $212.8227   $212.82   $212.80   $212.80  
  7 purchase totals = $837.79       $891.4279   $891.43   $891.45   $891.50