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 $160.82   11.263%   $178.9332   $178.93   $178.95   $178.90  
  Purchase #2 $63.34   10.460%   $69.9654   $69.97   $69.95   $70.00  
  Purchase #3 $153.60   11.617%   $171.4437   $171.44   $171.45   $171.40  
  Purchase #4 $214.45   6.602%   $228.608   $228.61   $228.60   $228.60  
  Purchase #5 $246.97   8.184%   $267.182   $267.18   $267.20   $267.20  
  Purchase #6 $120.51   4.519%   $125.9558   $125.96   $125.95   $126.00  
  Purchase #7 $15.83   11.850%   $17.7059   $17.71   $17.70   $17.70  
  7 purchase totals = $975.52       $1,059.7940   $1,059.80   $1,059.80   $1,059.80