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 $212.63   7.347%   $228.2519   $228.25   $228.25   $228.30  
  Purchase #2 $95.84   11.548%   $106.9076   $106.91   $106.90   $106.90  
  Purchase #3 $213.99   12.299%   $240.3086   $240.31   $240.30   $240.30  
  Purchase #4 $183.92   4.241%   $191.72   $191.72   $191.70   $191.70  
  Purchase #5 $59.29   13.310%   $67.1815   $67.18   $67.20   $67.20  
  Purchase #6 $116.71   6.553%   $124.358   $124.36   $124.35   $124.40  
  Purchase #7 $152.57   3.306%   $157.614   $157.61   $157.60   $157.60  
  7 purchase totals = $1,034.95       $1,116.3416   $1,116.34   $1,116.30   $1,116.40