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 $54.62   9.263%   $59.6795   $59.68   $59.70   $59.70  
  Purchase #2 $76.88   10.800%   $85.183   $85.18   $85.20   $85.20  
  Purchase #3 $139.78   6.112%   $148.3234   $148.32   $148.30   $148.30  
  Purchase #4 $132.64   5.195%   $139.5306   $139.53   $139.55   $139.50  
  Purchase #5 $99.40   10.634%   $109.9702   $109.97   $109.95   $110.00  
  Purchase #6 $223.57   4.749%   $234.1873   $234.19   $234.20   $234.20  
  Purchase #7 $247.44   5.653%   $261.4278   $261.43   $261.45   $261.40  
  7 purchase totals = $974.33       $1,038.3018   $1,038.30   $1,038.35   $1,038.30