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 $58.44   6.748%   $62.3835   $62.38   $62.40   $62.40  
  Purchase #2 $167.52   9.789%   $183.9185   $183.92   $183.90   $183.90  
  Purchase #3 $138.28   12.209%   $155.1626   $155.16   $155.15   $155.20  
  Purchase #4 $33.64   12.662%   $37.8995   $37.90   $37.90   $37.90  
  Purchase #5 $79.78   11.353%   $88.8374   $88.84   $88.85   $88.80  
  Purchase #6 $193.54   4.233%   $201.7325   $201.73   $201.75   $201.70  
  Purchase #7 $50.93   9.457%   $55.7465   $55.75   $55.75   $55.70  
  7 purchase totals = $722.13       $785.6805   $785.68   $785.70   $785.60