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 $218.37   10.627%   $241.5762   $241.58   $241.60   $241.60  
  Purchase #2 $72.57   5.761%   $76.7508   $76.75   $76.75   $76.80  
  Purchase #3 $38.59   7.576%   $41.5136   $41.51   $41.50   $41.50  
  Purchase #4 $119.61   12.434%   $134.4823   $134.48   $134.50   $134.50  
  Purchase #5 $241.45   9.795%   $265.1   $265.10   $265.10   $265.10  
  Purchase #6 $31.80   3.220%   $32.824   $32.82   $32.80   $32.80  
  Purchase #7 $146.72   11.154%   $163.0851   $163.09   $163.10   $163.10  
  7 purchase totals = $869.11       $955.3320   $955.33   $955.35   $955.40