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 $146.57   6.413%   $155.9695   $155.97   $155.95   $156.00  
  Purchase #2 $58.31   10.452%   $64.4046   $64.40   $64.40   $64.40  
  Purchase #3 $205.74   11.781%   $229.9782   $229.98   $230.00   $230.00  
  Purchase #4 $16.27   6.616%   $17.3464   $17.35   $17.35   $17.30  
  Purchase #5 $139.87   5.314%   $147.3027   $147.30   $147.30   $147.30  
  Purchase #6 $152.86   11.801%   $170.899   $170.90   $170.90   $170.90  
  Purchase #7 $22.91   12.141%   $25.6915   $25.69   $25.70   $25.70  
  7 purchase totals = $742.53       $811.5919   $811.59   $811.60   $811.60