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 $127.55   10.817%   $141.3471   $141.35   $141.35   $141.30  
  Purchase #2 $11.85   6.358%   $12.6034   $12.60   $12.60   $12.60  
  Purchase #3 $29.71   7.413%   $31.9124   $31.91   $31.90   $31.90  
  Purchase #4 $68.42   3.251%   $70.6443   $70.64   $70.65   $70.60  
  Purchase #5 $203.79   13.110%   $230.5069   $230.51   $230.50   $230.50  
  Purchase #6 $98.26   7.832%   $105.9557   $105.96   $105.95   $106.00  
  Purchase #7 $159.76   12.215%   $179.2747   $179.27   $179.25   $179.30  
  7 purchase totals = $699.34       $772.2445   $772.24   $772.20   $772.20