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 $204.59   11.766%   $228.6621   $228.66   $228.65   $228.70  
  Purchase #2 $212.68   5.767%   $224.9453   $224.95   $224.95   $224.90  
  Purchase #3 $250.32   5.740%   $264.6884   $264.69   $264.70   $264.70  
  Purchase #4 $183.77   7.161%   $196.9298   $196.93   $196.95   $196.90  
  Purchase #5 $166.87   6.105%   $177.0574   $177.06   $177.05   $177.10  
  Purchase #6 $116.43   4.272%   $121.4039   $121.40   $121.40   $121.40  
  Purchase #7 $135.76   6.784%   $144.97   $144.97   $144.95   $145.00  
  7 purchase totals = $1,270.42       $1,358.6569   $1,358.66   $1,358.65   $1,358.70