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 $106.61   6.861%   $113.9245   $113.92   $113.90   $113.90  
  Purchase #2 $58.45   3.349%   $60.4075   $60.41   $60.40   $60.40  
  Purchase #3 $158.41   7.493%   $170.2797   $170.28   $170.30   $170.30  
  Purchase #4 $203.58   13.610%   $231.2872   $231.29   $231.30   $231.30  
  Purchase #5 $80.82   6.332%   $85.9375   $85.94   $85.95   $85.90  
  Purchase #6 $189.28   11.810%   $211.634   $211.63   $211.65   $211.60  
  Purchase #7 $236.30   6.854%   $252.496   $252.50   $252.50   $252.50  
  7 purchase totals = $1,033.45       $1,125.9664   $1,125.97   $1,126.00   $1,125.90