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 $42.77   11.194%   $47.5577   $47.56   $47.55   $47.60  
  Purchase #2 $181.72   10.388%   $200.5971   $200.60   $200.60   $200.60  
  Purchase #3 $239.84   7.596%   $258.0582   $258.06   $258.05   $258.10  
  Purchase #4 $23.27   7.106%   $24.9236   $24.92   $24.90   $24.90  
  Purchase #5 $209.51   8.529%   $227.3791   $227.38   $227.40   $227.40  
  Purchase #6 $150.46   8.499%   $163.2476   $163.25   $163.25   $163.20  
  Purchase #7 $93.28   11.205%   $103.732   $103.73   $103.75   $103.70  
  7 purchase totals = $940.85       $1,025.4953   $1,025.50   $1,025.50   $1,025.50