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 $50.81   8.139%   $54.9454   $54.95   $54.95   $54.90  
  Purchase #2 $198.78   4.637%   $207.9974   $208.00   $208.00   $208.00  
  Purchase #3 $79.88   10.764%   $88.4783   $88.48   $88.50   $88.50  
  Purchase #4 $171.99   11.279%   $191.3888   $191.39   $191.40   $191.40  
  Purchase #5 $150.28   10.155%   $165.5409   $165.54   $165.55   $165.50  
  Purchase #6 $6.75   12.492%   $7.5932   $7.59   $7.60   $7.60  
  Purchase #7 $145.47   8.790%   $158.2568   $158.26   $158.25   $158.30  
  7 purchase totals = $803.96       $874.2008   $874.21   $874.25   $874.20