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 $45.63   6.126%   $48.4253   $48.43   $48.45   $48.40  
  Purchase #2 $167.68   5.261%   $176.5016   $176.50   $176.50   $176.50  
  Purchase #3 $148.80   6.392%   $158.3113   $158.31   $158.30   $158.30  
  Purchase #4 $175.80   4.126%   $183.0535   $183.05   $183.05   $183.10  
  Purchase #5 $121.28   8.832%   $131.9914   $131.99   $132.00   $132.00  
  Purchase #6 $99.87   7.448%   $107.3083   $107.31   $107.30   $107.30  
  Purchase #7 $214.95   6.264%   $228.4145   $228.41   $228.40   $228.40  
  7 purchase totals = $974.01       $1,034.0059   $1,034.00   $1,034.00   $1,034.00