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 $124.57   10.220%   $137.3011   $137.30   $137.30   $137.30  
  Purchase #2 $89.73   8.826%   $97.6496   $97.65   $97.65   $97.60  
  Purchase #3 $80.94   4.608%   $84.6697   $84.67   $84.65   $84.70  
  Purchase #4 $87.95   8.490%   $95.417   $95.42   $95.40   $95.40  
  Purchase #5 $168.38   13.451%   $191.0288   $191.03   $191.05   $191.00  
  Purchase #6 $183.91   6.281%   $195.4614   $195.46   $195.45   $195.50  
  Purchase #7 $195.70   6.454%   $208.3305   $208.33   $208.35   $208.30  
  7 purchase totals = $931.18       $1,009.8581   $1,009.86   $1,009.85   $1,009.80