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 $58.52   6.613%   $62.3899   $62.39   $62.40   $62.40  
  Purchase #2 $123.67   5.808%   $130.8528   $130.85   $130.85   $130.90  
  Purchase #3 $45.53   9.682%   $49.9382   $49.94   $49.95   $49.90  
  Purchase #4 $240.50   7.346%   $258.1671   $258.17   $258.15   $258.20  
  Purchase #5 $49.58   5.402%   $52.2583   $52.26   $52.25   $52.30  
  Purchase #6 $177.98   8.521%   $193.1457   $193.15   $193.15   $193.10  
  Purchase #7 $246.47   3.366%   $254.7662   $254.77   $254.75   $254.80  
  7 purchase totals = $942.25       $1,001.5182   $1,001.53   $1,001.50   $1,001.60