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 $46.57   6.457%   $49.577   $49.58   $49.60   $49.60  
  Purchase #2 $206.62   5.831%   $218.668   $218.67   $218.65   $218.70  
  Purchase #3 $47.78   9.446%   $52.2933   $52.29   $52.30   $52.30  
  Purchase #4 $164.98   11.431%   $183.8389   $183.84   $183.85   $183.80  
  Purchase #5 $162.61   11.298%   $180.9817   $180.98   $181.00   $181.00  
  Purchase #6 $97.93   6.136%   $103.939   $103.94   $103.95   $103.90  
  Purchase #7 $178.35   4.793%   $186.8983   $186.90   $186.90   $186.90  
  7 purchase totals = $904.84       $976.1962   $976.20   $976.25   $976.20