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 $50.54   5.802%   $53.4723   $53.47   $53.45   $53.50  
  Purchase #2 $219.26   4.150%   $228.3593   $228.36   $228.35   $228.40  
  Purchase #3 $223.66   5.383%   $235.6996   $235.70   $235.70   $235.70  
  Purchase #4 $47.41   7.770%   $51.0938   $51.09   $51.10   $51.10  
  Purchase #5 $160.81   9.573%   $176.2043   $176.20   $176.20   $176.20  
  Purchase #6 $50.30   4.416%   $52.5212   $52.52   $52.50   $52.50  
  Purchase #7 $233.54   5.369%   $246.0788   $246.08   $246.10   $246.10  
  7 purchase totals = $985.52       $1,043.4293   $1,043.42   $1,043.40   $1,043.50