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 $71.33   5.785%   $75.4564   $75.46   $75.45   $75.50  
  Purchase #2 $120.60   3.630%   $124.9778   $124.98   $125.00   $125.00  
  Purchase #3 $40.30   9.535%   $44.1426   $44.14   $44.15   $44.10  
  Purchase #4 $210.94   5.461%   $222.4594   $222.46   $222.45   $222.50  
  Purchase #5 $142.78   8.356%   $154.7107   $154.71   $154.70   $154.70  
  Purchase #6 $145.27   7.263%   $155.821   $155.82   $155.80   $155.80  
  Purchase #7 $246.25   10.186%   $271.333   $271.33   $271.35   $271.30  
  7 purchase totals = $977.47       $1,048.9009   $1,048.90   $1,048.90   $1,048.90