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 $228.26   5.835%   $241.579   $241.58   $241.60   $241.60  
  Purchase #2 $156.39   9.599%   $171.4019   $171.40   $171.40   $171.40  
  Purchase #3 $232.95   8.433%   $252.5947   $252.59   $252.60   $252.60  
  Purchase #4 $167.79   11.388%   $186.8979   $186.90   $186.90   $186.90  
  Purchase #5 $53.89   13.130%   $60.9658   $60.97   $60.95   $61.00  
  Purchase #6 $31.70   3.400%   $32.7778   $32.78   $32.80   $32.80  
  Purchase #7 $72.98   9.163%   $79.6672   $79.67   $79.65   $79.70  
  7 purchase totals = $943.96       $1,025.8843   $1,025.89   $1,025.90   $1,026.00