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 $105.96   12.873%   $119.6002   $119.60   $119.60   $119.60  
  Purchase #2 $167.44   3.716%   $173.6621   $173.66   $173.65   $173.70  
  Purchase #3 $75.87   5.320%   $79.9063   $79.91   $79.90   $79.90  
  Purchase #4 $56.77   7.108%   $60.8052   $60.81   $60.80   $60.80  
  Purchase #5 $169.81   6.309%   $180.5233   $180.52   $180.50   $180.50  
  Purchase #6 $225.70   4.408%   $235.6489   $235.65   $235.65   $235.60  
  Purchase #7 $132.44   8.869%   $144.1861   $144.19   $144.20   $144.20  
  7 purchase totals = $933.99       $994.3321   $994.34   $994.30   $994.30