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 $62.32   12.746%   $70.2633   $70.26   $70.25   $70.30  
  Purchase #2 $183.37   8.218%   $198.4393   $198.44   $198.45   $198.40  
  Purchase #3 $236.88   8.117%   $256.1075   $256.11   $256.10   $256.10  
  Purchase #4 $90.59   12.733%   $102.1248   $102.12   $102.10   $102.10  
  Purchase #5 $47.89   6.135%   $50.8281   $50.83   $50.85   $50.80  
  Purchase #6 $93.57   12.564%   $105.3261   $105.33   $105.35   $105.30  
  Purchase #7 $113.32   4.471%   $118.3865   $118.39   $118.40   $118.40  
  7 purchase totals = $827.94       $901.4756   $901.48   $901.50   $901.40