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 $62.72   4.199%   $65.3536   $65.35   $65.35   $65.40  
  Purchase #2 $231.38   12.381%   $260.0272   $260.03   $260.05   $260.00  
  Purchase #3 $54.25   8.752%   $58.998   $59.00   $59.00   $59.00  
  Purchase #4 $152.66   6.133%   $162.0226   $162.02   $162.00   $162.00  
  Purchase #5 $203.41   13.486%   $230.8419   $230.84   $230.85   $230.80  
  Purchase #6 $56.41   9.291%   $61.6511   $61.65   $61.65   $61.70  
  Purchase #7 $106.30   8.240%   $115.0591   $115.06   $115.05   $115.10  
  7 purchase totals = $867.13       $953.9535   $953.95   $953.95   $954.00