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 $60.67   13.854%   $69.0752   $69.08   $69.10   $69.10  
  Purchase #2 $158.79   6.621%   $169.3035   $169.30   $169.30   $169.30  
  Purchase #3 $116.70   5.837%   $123.5118   $123.51   $123.50   $123.50  
  Purchase #4 $133.59   9.625%   $146.448   $146.45   $146.45   $146.40  
  Purchase #5 $203.26   12.227%   $228.1126   $228.11   $228.10   $228.10  
  Purchase #6 $84.96   5.219%   $89.3941   $89.39   $89.40   $89.40  
  Purchase #7 $14.53   12.322%   $16.3204   $16.32   $16.30   $16.30  
  7 purchase totals = $772.50       $842.1656   $842.16   $842.15   $842.10