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 $60.27   12.256%   $67.6567   $67.66   $67.65   $67.70  
  Purchase #2 $117.67   9.265%   $128.5721   $128.57   $128.55   $128.60  
  Purchase #3 $156.47   11.614%   $174.6424   $174.64   $174.65   $174.60  
  Purchase #4 $241.34   11.757%   $269.7143   $269.71   $269.70   $269.70  
  Purchase #5 $119.69   8.415%   $129.7619   $129.76   $129.75   $129.80  
  Purchase #6 $248.62   4.708%   $260.325   $260.33   $260.35   $260.30  
  Purchase #7 $41.80   12.620%   $47.0752   $47.08   $47.10   $47.10  
  7 purchase totals = $985.86       $1,077.7476   $1,077.75   $1,077.75   $1,077.80