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 $62.67   9.772%   $68.7941   $68.79   $68.80   $68.80  
  Purchase #2 $89.55   4.598%   $93.6675   $93.67   $93.65   $93.70  
  Purchase #3 $170.41   9.286%   $186.2343   $186.23   $186.25   $186.20  
  Purchase #4 $94.31   5.763%   $99.7451   $99.75   $99.75   $99.70  
  Purchase #5 $41.47   4.713%   $43.4245   $43.42   $43.40   $43.40  
  Purchase #6 $23.46   11.848%   $26.2395   $26.24   $26.25   $26.20  
  Purchase #7 $110.87   4.154%   $115.4755   $115.48   $115.50   $115.50  
  7 purchase totals = $592.74       $633.5805   $633.58   $633.60   $633.50