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 $63.96   8.794%   $69.5846   $69.58   $69.60   $69.60  
  Purchase #2 $141.78   4.845%   $148.6492   $148.65   $148.65   $148.60  
  Purchase #3 $66.65   4.294%   $69.512   $69.51   $69.50   $69.50  
  Purchase #4 $92.96   8.782%   $101.1237   $101.12   $101.10   $101.10  
  Purchase #5 $232.46   6.850%   $248.3835   $248.38   $248.40   $248.40  
  Purchase #6 $12.94   12.300%   $14.5316   $14.53   $14.55   $14.50  
  Purchase #7 $24.87   7.547%   $26.7469   $26.75   $26.75   $26.70  
  7 purchase totals = $635.62       $678.5315   $678.52   $678.55   $678.40