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 $129.74   5.841%   $137.3181   $137.32   $137.30   $137.30  
  Purchase #2 $76.87   5.587%   $81.1647   $81.16   $81.15   $81.20  
  Purchase #3 $162.26   5.786%   $171.6484   $171.65   $171.65   $171.60  
  Purchase #4 $235.57   4.644%   $246.5099   $246.51   $246.50   $246.50  
  Purchase #5 $118.44   3.670%   $122.7867   $122.79   $122.80   $122.80  
  Purchase #6 $247.31   12.216%   $277.5214   $277.52   $277.50   $277.50  
  Purchase #7 $23.31   6.199%   $24.755   $24.76   $24.75   $24.80  
  7 purchase totals = $993.50       $1,061.7042   $1,061.71   $1,061.65   $1,061.70