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 $68.74   12.803%   $77.5408   $77.54   $77.55   $77.50  
  Purchase #2 $220.50   7.543%   $237.1323   $237.13   $237.15   $237.10  
  Purchase #3 $27.29   11.827%   $30.5176   $30.52   $30.50   $30.50  
  Purchase #4 $55.54   9.598%   $60.8707   $60.87   $60.85   $60.90  
  Purchase #5 $243.82   8.603%   $264.7958   $264.80   $264.80   $264.80  
  Purchase #6 $246.52   13.145%   $278.9251   $278.93   $278.95   $278.90  
  Purchase #7 $70.83   4.781%   $74.2164   $74.22   $74.20   $74.20  
  7 purchase totals = $933.24       $1,023.9987   $1,024.01   $1,024.00   $1,023.90