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 $30.48   13.442%   $34.5771   $34.58   $34.60   $34.60  
  Purchase #2 $205.83   9.334%   $225.0422   $225.04   $225.05   $225.00  
  Purchase #3 $114.96   8.424%   $124.6442   $124.64   $124.65   $124.60  
  Purchase #4 $140.98   7.660%   $151.7791   $151.78   $151.80   $151.80  
  Purchase #5 $215.77   3.247%   $222.7761   $222.78   $222.80   $222.80  
  Purchase #6 $29.85   10.543%   $32.9971   $33.00   $33.00   $33.00  
  Purchase #7 $204.63   7.798%   $220.587   $220.59   $220.60   $220.60  
  7 purchase totals = $942.50       $1,012.4028   $1,012.41   $1,012.50   $1,012.40