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 $248.28   6.625%   $264.7286   $264.73   $264.75   $264.70  
  Purchase #2 $226.62   4.327%   $236.4258   $236.43   $236.45   $236.40  
  Purchase #3 $99.74   3.519%   $103.2499   $103.25   $103.25   $103.20  
  Purchase #4 $100.94   3.598%   $104.5718   $104.57   $104.55   $104.60  
  Purchase #5 $11.76   6.793%   $12.5589   $12.56   $12.55   $12.60  
  Purchase #6 $192.74   4.636%   $201.6754   $201.68   $201.70   $201.70  
  Purchase #7 $21.28   13.474%   $24.1473   $24.15   $24.15   $24.10  
  7 purchase totals = $901.36       $947.3577   $947.37   $947.40   $947.30