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 $63.96   6.304%   $67.992   $67.99   $68.00   $68.00  
  Purchase #2 $45.73   5.545%   $48.2657   $48.27   $48.25   $48.30  
  Purchase #3 $77.43   4.182%   $80.6681   $80.67   $80.65   $80.70  
  Purchase #4 $222.34   3.517%   $230.1597   $230.16   $230.15   $230.20  
  Purchase #5 $145.89   7.742%   $157.1848   $157.18   $157.20   $157.20  
  Purchase #6 $180.28   6.713%   $192.3822   $192.38   $192.40   $192.40  
  Purchase #7 $218.80   5.447%   $230.718   $230.72   $230.70   $230.70  
  7 purchase totals = $954.43       $1,007.3705   $1,007.37   $1,007.35   $1,007.50