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 $58.49   3.250%   $60.3909   $60.39   $60.40   $60.40  
  Purchase #2 $174.77   7.755%   $188.3234   $188.32   $188.30   $188.30  
  Purchase #3 $21.95   9.279%   $23.9867   $23.99   $24.00   $24.00  
  Purchase #4 $70.31   6.636%   $74.9758   $74.98   $75.00   $75.00  
  Purchase #5 $247.55   11.741%   $276.6148   $276.61   $276.60   $276.60  
  Purchase #6 $198.36   11.158%   $220.493   $220.49   $220.50   $220.50  
  Purchase #7 $167.31   12.398%   $188.0531   $188.05   $188.05   $188.10  
  7 purchase totals = $938.74       $1,032.8377   $1,032.83   $1,032.85   $1,032.90