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 $58.26   6.292%   $61.9257   $61.93   $61.95   $61.90  
  Purchase #2 $208.30   7.564%   $224.0558   $224.06   $224.05   $224.10  
  Purchase #3 $148.94   11.199%   $165.6198   $165.62   $165.60   $165.60  
  Purchase #4 $11.83   6.239%   $12.5681   $12.57   $12.55   $12.60  
  Purchase #5 $38.39   12.235%   $43.087   $43.09   $43.10   $43.10  
  Purchase #6 $169.72   12.251%   $190.5124   $190.51   $190.50   $190.50  
  Purchase #7 $66.65   3.490%   $68.9761   $68.98   $69.00   $69.00  
  7 purchase totals = $702.09       $766.7449   $766.76   $766.75   $766.80