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 $44.48   12.169%   $49.8928   $49.89   $49.90   $49.90  
  Purchase #2 $176.33   4.378%   $184.0497   $184.05   $184.05   $184.00  
  Purchase #3 $171.36   13.584%   $194.6375   $194.64   $194.65   $194.60  
  Purchase #4 $239.70   3.347%   $247.7228   $247.72   $247.70   $247.70  
  Purchase #5 $218.93   5.294%   $230.5202   $230.52   $230.50   $230.50  
  Purchase #6 $54.64   8.682%   $59.3838   $59.38   $59.40   $59.40  
  Purchase #7 $57.28   6.270%   $60.8715   $60.87   $60.85   $60.90  
  7 purchase totals = $962.72       $1,027.0783   $1,027.07   $1,027.05   $1,027.00