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 $117.75   5.270%   $123.9554   $123.96   $123.95   $124.00  
  Purchase #2 $181.80   11.601%   $202.8906   $202.89   $202.90   $202.90  
  Purchase #3 $20.86   5.489%   $22.005   $22.01   $22.00   $22.00  
  Purchase #4 $68.44   9.707%   $75.0835   $75.08   $75.10   $75.10  
  Purchase #5 $101.27   6.168%   $107.5163   $107.52   $107.50   $107.50  
  Purchase #6 $247.63   4.174%   $257.9661   $257.97   $257.95   $258.00  
  Purchase #7 $12.76   9.618%   $13.9873   $13.99   $14.00   $14.00  
  7 purchase totals = $750.51       $803.4042   $803.42   $803.40   $803.50