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 $115.51   3.728%   $119.8162   $119.82   $119.80   $119.80  
  Purchase #2 $12.72   13.580%   $14.4474   $14.45   $14.45   $14.40  
  Purchase #3 $184.83   4.196%   $192.5855   $192.59   $192.60   $192.60  
  Purchase #4 $96.58   11.817%   $107.9929   $107.99   $108.00   $108.00  
  Purchase #5 $162.46   6.585%   $173.158   $173.16   $173.15   $173.20  
  Purchase #6 $121.65   10.568%   $134.506   $134.51   $134.50   $134.50  
  Purchase #7 $215.91   7.464%   $232.0255   $232.03   $232.05   $232.00  
  7 purchase totals = $909.66       $974.5315   $974.55   $974.55   $974.50