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 $54.26   12.522%   $61.0544   $61.05   $61.05   $61.10  
  Purchase #2 $171.96   12.505%   $193.4636   $193.46   $193.45   $193.50  
  Purchase #3 $47.33   7.700%   $50.9744   $50.97   $50.95   $51.00  
  Purchase #4 $225.63   6.737%   $240.8307   $240.83   $240.85   $240.80  
  Purchase #5 $148.29   12.411%   $166.6943   $166.69   $166.70   $166.70  
  Purchase #6 $41.92   12.836%   $47.3009   $47.30   $47.30   $47.30  
  Purchase #7 $190.99   5.851%   $202.1648   $202.16   $202.15   $202.20  
  7 purchase totals = $880.38       $962.4831   $962.46   $962.45   $962.60