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 $58.97   3.578%   $61.0799   $61.08   $61.10   $61.10  
  Purchase #2 $200.73   8.813%   $218.4203   $218.42   $218.40   $218.40  
  Purchase #3 $102.52   12.350%   $115.1812   $115.18   $115.20   $115.20  
  Purchase #4 $144.74   5.657%   $152.9279   $152.93   $152.95   $152.90  
  Purchase #5 $227.28   3.562%   $235.3757   $235.38   $235.40   $235.40  
  Purchase #6 $248.44   10.360%   $274.1784   $274.18   $274.20   $274.20  
  Purchase #7 $71.94   13.437%   $81.6066   $81.61   $81.60   $81.60  
  7 purchase totals = $1,054.62       $1,138.7700   $1,138.78   $1,138.85   $1,138.80