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 $52.33   11.589%   $58.3945   $58.39   $58.40   $58.40  
  Purchase #2 $241.98   9.517%   $265.0092   $265.01   $265.00   $265.00  
  Purchase #3 $56.28   3.663%   $58.3415   $58.34   $58.35   $58.30  
  Purchase #4 $153.81   11.713%   $171.8258   $171.83   $171.85   $171.80  
  Purchase #5 $102.64   11.188%   $114.1234   $114.12   $114.10   $114.10  
  Purchase #6 $228.73   12.616%   $257.5866   $257.59   $257.60   $257.60  
  Purchase #7 $219.32   12.170%   $246.0112   $246.01   $246.00   $246.00  
  7 purchase totals = $1,055.09       $1,171.2922   $1,171.29   $1,171.30   $1,171.20