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 $74.95   13.434%   $85.0188   $85.02   $85.00   $85.00  
  Purchase #2 $194.55   8.783%   $211.6373   $211.64   $211.65   $211.60  
  Purchase #3 $67.42   7.565%   $72.5203   $72.52   $72.50   $72.50  
  Purchase #4 $104.89   4.848%   $109.9751   $109.98   $110.00   $110.00  
  Purchase #5 $24.96   8.196%   $27.0057   $27.01   $27.00   $27.00  
  Purchase #6 $143.38   12.439%   $161.215   $161.22   $161.20   $161.20  
  Purchase #7 $188.48   11.526%   $210.2042   $210.20   $210.20   $210.20  
  7 purchase totals = $798.63       $877.5764   $877.59   $877.55   $877.50