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 $37.52   3.816%   $38.9518   $38.95   $38.95   $39.00  
  Purchase #2 $247.83   11.760%   $276.9748   $276.97   $276.95   $277.00  
  Purchase #3 $58.25   5.279%   $61.325   $61.33   $61.35   $61.30  
  Purchase #4 $118.46   5.236%   $124.6626   $124.66   $124.65   $124.70  
  Purchase #5 $160.50   10.516%   $177.3782   $177.38   $177.40   $177.40  
  Purchase #6 $89.34   6.170%   $94.8523   $94.85   $94.85   $94.90  
  Purchase #7 $194.35   10.664%   $215.0755   $215.08   $215.10   $215.10  
  7 purchase totals = $906.25       $989.2202   $989.22   $989.25   $989.40