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 $56.74   7.542%   $61.0193   $61.02   $61.00   $61.00  
  Purchase #2 $31.58   4.827%   $33.1044   $33.10   $33.10   $33.10  
  Purchase #3 $244.37   4.395%   $255.1101   $255.11   $255.10   $255.10  
  Purchase #4 $234.96   11.630%   $262.2858   $262.29   $262.30   $262.30  
  Purchase #5 $241.74   8.689%   $262.7448   $262.74   $262.75   $262.70  
  Purchase #6 $9.64   9.784%   $10.5832   $10.58   $10.60   $10.60  
  Purchase #7 $70.83   6.665%   $75.5508   $75.55   $75.55   $75.60  
  7 purchase totals = $889.86       $960.3984   $960.39   $960.40   $960.40