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 $169.50   4.771%   $177.5868   $177.59   $177.60   $177.60  
  Purchase #2 $111.83   11.474%   $124.6614   $124.66   $124.65   $124.70  
  Purchase #3 $191.25   5.471%   $201.7133   $201.71   $201.70   $201.70  
  Purchase #4 $11.41   13.433%   $12.9427   $12.94   $12.95   $12.90  
  Purchase #5 $218.60   12.591%   $246.1239   $246.12   $246.10   $246.10  
  Purchase #6 $204.49   10.422%   $225.8019   $225.80   $225.80   $225.80  
  Purchase #7 $151.46   3.194%   $156.2976   $156.30   $156.30   $156.30  
  7 purchase totals = $1,058.54       $1,145.1276   $1,145.12   $1,145.10   $1,145.10