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 $177.84   8.525%   $193.0009   $193.00   $193.00   $193.00  
  Purchase #2 $24.32   6.861%   $25.9886   $25.99   $26.00   $26.00  
  Purchase #3 $209.36   13.209%   $237.0144   $237.01   $237.00   $237.00  
  Purchase #4 $170.70   9.284%   $186.5478   $186.55   $186.55   $186.50  
  Purchase #5 $246.94   5.388%   $260.2451   $260.25   $260.25   $260.20  
  Purchase #6 $192.83   13.794%   $219.429   $219.43   $219.45   $219.40  
  Purchase #7 $58.93   9.444%   $64.4953   $64.50   $64.50   $64.50  
  7 purchase totals = $1,080.92       $1,186.7211   $1,186.73   $1,186.75   $1,186.60