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 $139.55   8.133%   $150.8996   $150.90   $150.90   $150.90  
  Purchase #2 $178.35   8.392%   $193.3171   $193.32   $193.30   $193.30  
  Purchase #3 $111.92   10.109%   $123.234   $123.23   $123.25   $123.20  
  Purchase #4 $182.27   5.363%   $192.0451   $192.05   $192.05   $192.00  
  Purchase #5 $115.35   3.611%   $119.5153   $119.52   $119.50   $119.50  
  Purchase #6 $209.78   9.163%   $229.0021   $229.00   $229.00   $229.00  
  Purchase #7 $242.51   5.542%   $255.9499   $255.95   $255.95   $255.90  
  7 purchase totals = $1,179.73       $1,263.9631   $1,263.97   $1,263.95   $1,263.80