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 $104.74   11.847%   $117.1485   $117.15   $117.15   $117.10  
  Purchase #2 $168.45   3.646%   $174.5917   $174.59   $174.60   $174.60  
  Purchase #3 $102.68   4.698%   $107.5039   $107.50   $107.50   $107.50  
  Purchase #4 $246.94   12.158%   $276.963   $276.96   $276.95   $277.00  
  Purchase #5 $200.89   3.487%   $207.895   $207.90   $207.90   $207.90  
  Purchase #6 $165.30   10.333%   $182.3804   $182.38   $182.40   $182.40  
  Purchase #7 $68.82   6.217%   $73.0985   $73.10   $73.10   $73.10  
  7 purchase totals = $1,057.82       $1,139.5810   $1,139.58   $1,139.60   $1,139.60