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 $41.43   11.271%   $46.0996   $46.10   $46.10   $46.10  
  Purchase #2 $140.91   3.377%   $145.6685   $145.67   $145.65   $145.70  
  Purchase #3 $196.58   10.121%   $216.4759   $216.48   $216.50   $216.50  
  Purchase #4 $33.70   13.730%   $38.327   $38.33   $38.35   $38.30  
  Purchase #5 $10.76   13.398%   $12.2016   $12.20   $12.20   $12.20  
  Purchase #6 $250.35   3.167%   $258.2786   $258.28   $258.30   $258.30  
  Purchase #7 $92.64   3.117%   $95.5276   $95.53   $95.55   $95.50  
  7 purchase totals = $766.37       $812.5788   $812.59   $812.65   $812.60