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 $88.86   8.729%   $96.6166   $96.62   $96.60   $96.60  
  Purchase #2 $202.51   13.481%   $229.8104   $229.81   $229.80   $229.80  
  Purchase #3 $159.41   12.353%   $179.1019   $179.10   $179.10   $179.10  
  Purchase #4 $152.95   5.587%   $161.4953   $161.50   $161.50   $161.50  
  Purchase #5 $63.71   13.321%   $72.1968   $72.20   $72.20   $72.20  
  Purchase #6 $188.37   4.855%   $197.5154   $197.52   $197.50   $197.50  
  Purchase #7 $154.81   11.111%   $172.0109   $172.01   $172.00   $172.00  
  7 purchase totals = $1,010.62       $1,108.7473   $1,108.76   $1,108.70   $1,108.70