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 $202.36   12.328%   $227.3069   $227.31   $227.30   $227.30  
  Purchase #2 $168.76   11.221%   $187.6966   $187.70   $187.70   $187.70  
  Purchase #3 $37.76   9.795%   $41.4586   $41.46   $41.45   $41.50  
  Purchase #4 $234.59   5.463%   $247.4057   $247.41   $247.40   $247.40  
  Purchase #5 $129.45   7.499%   $139.1575   $139.16   $139.15   $139.20  
  Purchase #6 $143.67   3.586%   $148.822   $148.82   $148.80   $148.80  
  Purchase #7 $35.87   9.643%   $39.3289   $39.33   $39.35   $39.30  
  7 purchase totals = $952.46       $1,031.1762   $1,031.19   $1,031.15   $1,031.20