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 $24.84   8.537%   $26.9606   $26.96   $26.95   $27.00  
  Purchase #2 $216.78   8.395%   $234.9787   $234.98   $235.00   $235.00  
  Purchase #3 $53.90   6.126%   $57.2019   $57.20   $57.20   $57.20  
  Purchase #4 $209.43   5.199%   $220.3183   $220.32   $220.30   $220.30  
  Purchase #5 $156.65   13.852%   $178.3492   $178.35   $178.35   $178.30  
  Purchase #6 $80.70   12.565%   $90.84   $90.84   $90.85   $90.80  
  Purchase #7 $171.50   3.326%   $177.2041   $177.20   $177.20   $177.20  
  7 purchase totals = $913.80       $985.8528   $985.85   $985.85   $985.80