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 $86.51   7.740%   $93.2059   $93.21   $93.20   $93.20  
  Purchase #2 $122.95   10.225%   $135.5216   $135.52   $135.50   $135.50  
  Purchase #3 $213.93   8.691%   $232.5227   $232.52   $232.50   $232.50  
  Purchase #4 $114.95   9.742%   $126.1484   $126.15   $126.15   $126.10  
  Purchase #5 $184.87   7.459%   $198.6595   $198.66   $198.65   $198.70  
  Purchase #6 $121.75   11.726%   $136.0264   $136.03   $136.05   $136.00  
  Purchase #7 $126.46   5.350%   $133.2256   $133.23   $133.25   $133.20  
  7 purchase totals = $971.42       $1,055.3101   $1,055.32   $1,055.30   $1,055.20