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 $67.65   10.198%   $74.5489   $74.55   $74.55   $74.50  
  Purchase #2 $119.55   5.668%   $126.3261   $126.33   $126.35   $126.30  
  Purchase #3 $82.39   4.617%   $86.1939   $86.19   $86.20   $86.20  
  Purchase #4 $215.83   7.258%   $231.4949   $231.49   $231.50   $231.50  
  Purchase #5 $34.42   11.736%   $38.4595   $38.46   $38.45   $38.50  
  Purchase #6 $131.59   12.697%   $148.298   $148.30   $148.30   $148.30  
  Purchase #7 $202.55   12.782%   $228.4399   $228.44   $228.45   $228.40  
  7 purchase totals = $853.98       $933.7612   $933.76   $933.80   $933.70