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 $226.99   10.473%   $250.7627   $250.76   $250.75   $250.80  
  Purchase #2 $69.35   8.570%   $75.2933   $75.29   $75.30   $75.30  
  Purchase #3 $23.81   3.490%   $24.641   $24.64   $24.65   $24.60  
  Purchase #4 $237.48   4.254%   $247.5824   $247.58   $247.60   $247.60  
  Purchase #5 $163.59   6.445%   $174.1334   $174.13   $174.15   $174.10  
  Purchase #6 $134.77   12.244%   $151.2712   $151.27   $151.25   $151.30  
  Purchase #7 $225.40   11.638%   $251.6321   $251.63   $251.65   $251.60  
  7 purchase totals = $1,081.39       $1,175.3161   $1,175.30   $1,175.35   $1,175.30