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 $32.67   5.472%   $34.4577   $34.46   $34.45   $34.50  
  Purchase #2 $193.31   6.408%   $205.6973   $205.70   $205.70   $205.70  
  Purchase #3 $162.76   9.233%   $177.7876   $177.79   $177.80   $177.80  
  Purchase #4 $51.40   6.580%   $54.7821   $54.78   $54.80   $54.80  
  Purchase #5 $128.57   5.194%   $135.2479   $135.25   $135.25   $135.20  
  Purchase #6 $44.83   9.460%   $49.0709   $49.07   $49.05   $49.10  
  Purchase #7 $185.73   8.152%   $200.8707   $200.87   $200.85   $200.90  
  7 purchase totals = $799.27       $857.9142   $857.92   $857.90   $858.00