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 $28.38   13.809%   $32.299   $32.30   $32.30   $32.30  
  Purchase #2 $53.47   11.289%   $59.5062   $59.51   $59.50   $59.50  
  Purchase #3 $205.65   3.642%   $213.1398   $213.14   $213.15   $213.10  
  Purchase #4 $196.93   11.364%   $219.3091   $219.31   $219.30   $219.30  
  Purchase #5 $192.96   9.477%   $211.2468   $211.25   $211.25   $211.20  
  Purchase #6 $190.99   6.172%   $202.7779   $202.78   $202.80   $202.80  
  Purchase #7 $33.25   4.568%   $34.7689   $34.77   $34.75   $34.80  
  7 purchase totals = $901.63       $973.0477   $973.06   $973.05   $973.00