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 $228.52   11.452%   $254.6901   $254.69   $254.70   $254.70  
  Purchase #2 $22.79   4.528%   $23.8219   $23.82   $23.80   $23.80  
  Purchase #3 $196.68   11.803%   $219.8941   $219.89   $219.90   $219.90  
  Purchase #4 $9.39   12.585%   $10.5717   $10.57   $10.55   $10.60  
  Purchase #5 $231.39   5.437%   $243.9707   $243.97   $243.95   $244.00  
  Purchase #6 $81.26   4.482%   $84.9021   $84.90   $84.90   $84.90  
  Purchase #7 $24.62   7.182%   $26.3882   $26.39   $26.40   $26.40  
  7 purchase totals = $794.65       $864.2388   $864.23   $864.20   $864.30