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 $123.74   10.312%   $136.5001   $136.50   $136.50   $136.50  
  Purchase #2 $216.98   8.545%   $235.5209   $235.52   $235.50   $235.50  
  Purchase #3 $42.41   10.162%   $46.7197   $46.72   $46.70   $46.70  
  Purchase #4 $94.27   8.719%   $102.4894   $102.49   $102.50   $102.50  
  Purchase #5 $61.50   5.421%   $64.8339   $64.83   $64.85   $64.80  
  Purchase #6 $8.62   10.280%   $9.5061   $9.51   $9.50   $9.50  
  Purchase #7 $136.33   10.582%   $150.7564   $150.76   $150.75   $150.80  
  7 purchase totals = $683.85       $746.3265   $746.33   $746.30   $746.30