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 $231.87   13.437%   $263.0264   $263.03   $263.05   $263.00  
  Purchase #2 $216.98   13.415%   $246.0879   $246.09   $246.10   $246.10  
  Purchase #3 $81.62   5.817%   $86.3678   $86.37   $86.35   $86.40  
  Purchase #4 $231.83   13.171%   $262.3643   $262.36   $262.35   $262.40  
  Purchase #5 $48.93   12.230%   $54.9141   $54.91   $54.90   $54.90  
  Purchase #6 $157.72   3.397%   $163.0777   $163.08   $163.10   $163.10  
  Purchase #7 $170.34   3.484%   $176.2746   $176.27   $176.25   $176.30  
  7 purchase totals = $1,139.29       $1,252.1128   $1,252.11   $1,252.10   $1,252.20