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 $53.41   13.229%   $60.4756   $60.48   $60.50   $60.50  
  Purchase #2 $183.74   3.319%   $189.8383   $189.84   $189.85   $189.80  
  Purchase #3 $222.36   6.455%   $236.7133   $236.71   $236.70   $236.70  
  Purchase #4 $99.41   13.237%   $112.5689   $112.57   $112.55   $112.60  
  Purchase #5 $160.81   6.147%   $170.695   $170.70   $170.70   $170.70  
  Purchase #6 $137.83   11.353%   $153.4778   $153.48   $153.50   $153.50  
  Purchase #7 $118.43   10.556%   $130.9315   $130.93   $130.95   $130.90  
  7 purchase totals = $975.99       $1,054.7004   $1,054.71   $1,054.75   $1,054.70