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 $208.73   11.577%   $232.8947   $232.89   $232.90   $232.90  
  Purchase #2 $182.81   11.565%   $203.952   $203.95   $203.95   $204.00  
  Purchase #3 $87.26   9.814%   $95.8237   $95.82   $95.80   $95.80  
  Purchase #4 $32.64   5.653%   $34.4851   $34.49   $34.50   $34.50  
  Purchase #5 $25.82   6.157%   $27.4097   $27.41   $27.40   $27.40  
  Purchase #6 $224.84   10.112%   $247.5758   $247.58   $247.60   $247.60  
  Purchase #7 $11.39   7.502%   $12.2445   $12.24   $12.25   $12.20  
  7 purchase totals = $773.49       $854.3855   $854.38   $854.40   $854.40