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 $54.80   11.509%   $61.1069   $61.11   $61.10   $61.10  
  Purchase #2 $122.30   12.846%   $138.0107   $138.01   $138.00   $138.00  
  Purchase #3 $235.48   9.408%   $257.634   $257.63   $257.65   $257.60  
  Purchase #4 $64.93   3.239%   $67.0331   $67.03   $67.05   $67.00  
  Purchase #5 $37.52   4.816%   $39.327   $39.33   $39.35   $39.30  
  Purchase #6 $98.96   13.454%   $112.2741   $112.27   $112.25   $112.30  
  Purchase #7 $65.64   9.185%   $71.669   $71.67   $71.65   $71.70  
  7 purchase totals = $679.63       $747.0548   $747.05   $747.05   $747.00