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 $66.58   8.128%   $71.9916   $71.99   $72.00   $72.00  
  Purchase #2 $176.77   8.331%   $191.4967   $191.50   $191.50   $191.50  
  Purchase #3 $37.51   6.260%   $39.8581   $39.86   $39.85   $39.90  
  Purchase #4 $192.33   5.429%   $202.7716   $202.77   $202.75   $202.80  
  Purchase #5 $172.85   12.466%   $194.3975   $194.40   $194.40   $194.40  
  Purchase #6 $200.43   12.823%   $226.1311   $226.13   $226.15   $226.10  
  Purchase #7 $129.62   4.186%   $135.0459   $135.05   $135.05   $135.00  
  7 purchase totals = $976.09       $1,061.6925   $1,061.70   $1,061.70   $1,061.70