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 $203.70   11.569%   $227.2661   $227.27   $227.25   $227.30  
  Purchase #2 $121.42   4.319%   $126.6641   $126.66   $126.65   $126.70  
  Purchase #3 $169.77   11.626%   $189.5075   $189.51   $189.50   $189.50  
  Purchase #4 $187.66   9.484%   $205.4577   $205.46   $205.45   $205.50  
  Purchase #5 $50.84   11.490%   $56.6815   $56.68   $56.70   $56.70  
  Purchase #6 $137.65   12.135%   $154.3538   $154.35   $154.35   $154.40  
  Purchase #7 $228.81   8.681%   $248.673   $248.67   $248.65   $248.70  
  7 purchase totals = $1,099.85       $1,208.6037   $1,208.60   $1,208.55   $1,208.80