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 $199.53   13.521%   $226.5085   $226.51   $226.50   $226.50  
  Purchase #2 $76.31   6.573%   $81.3259   $81.33   $81.35   $81.30  
  Purchase #3 $120.80   4.527%   $126.2686   $126.27   $126.25   $126.30  
  Purchase #4 $148.95   9.610%   $163.2641   $163.26   $163.25   $163.30  
  Purchase #5 $94.31   13.521%   $107.0617   $107.06   $107.05   $107.10  
  Purchase #6 $165.35   7.444%   $177.6587   $177.66   $177.65   $177.70  
  Purchase #7 $168.43   7.686%   $181.3755   $181.38   $181.40   $181.40  
  7 purchase totals = $973.68       $1,063.4630   $1,063.47   $1,063.45   $1,063.60