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 $205.97   6.195%   $218.7298   $218.73   $218.75   $218.70  
  Purchase #2 $214.59   9.343%   $234.6391   $234.64   $234.65   $234.60  
  Purchase #3 $118.38   9.293%   $129.3811   $129.38   $129.40   $129.40  
  Purchase #4 $152.74   6.670%   $162.9278   $162.93   $162.95   $162.90  
  Purchase #5 $214.50   6.560%   $228.5712   $228.57   $228.55   $228.60  
  Purchase #6 $221.86   5.775%   $234.6724   $234.67   $234.65   $234.70  
  Purchase #7 $158.50   4.201%   $165.1586   $165.16   $165.15   $165.20  
  7 purchase totals = $1,286.54       $1,374.0800   $1,374.08   $1,374.10   $1,374.10