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 $241.82   8.526%   $262.4376   $262.44   $262.45   $262.40  
  Purchase #2 $170.78   12.111%   $191.4632   $191.46   $191.45   $191.50  
  Purchase #3 $96.96   11.784%   $108.3858   $108.39   $108.40   $108.40  
  Purchase #4 $216.75   7.182%   $232.317   $232.32   $232.30   $232.30  
  Purchase #5 $165.67   11.454%   $184.6458   $184.65   $184.65   $184.60  
  Purchase #6 $59.46   3.190%   $61.3568   $61.36   $61.35   $61.40  
  Purchase #7 $132.86   7.325%   $142.592   $142.59   $142.60   $142.60  
  7 purchase totals = $1,084.30       $1,183.1982   $1,183.21   $1,183.20   $1,183.20