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 $190.29   6.831%   $203.2887   $203.29   $203.30   $203.30  
  Purchase #2 $117.27   5.263%   $123.4419   $123.44   $123.45   $123.40  
  Purchase #3 $214.30   10.279%   $236.3279   $236.33   $236.35   $236.30  
  Purchase #4 $54.87   5.673%   $57.9828   $57.98   $58.00   $58.00  
  Purchase #5 $171.53   8.556%   $186.2061   $186.21   $186.20   $186.20  
  Purchase #6 $176.93   5.441%   $186.5568   $186.56   $186.55   $186.60  
  Purchase #7 $54.88   6.805%   $58.6146   $58.61   $58.60   $58.60  
  7 purchase totals = $980.07       $1,052.4188   $1,052.42   $1,052.45   $1,052.40