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 $200.96   11.787%   $224.6472   $224.65   $224.65   $224.60  
  Purchase #2 $41.36   8.134%   $44.7242   $44.72   $44.70   $44.70  
  Purchase #3 $46.77   8.127%   $50.571   $50.57   $50.55   $50.60  
  Purchase #4 $175.43   12.326%   $197.0535   $197.05   $197.05   $197.10  
  Purchase #5 $130.38   13.461%   $147.9305   $147.93   $147.95   $147.90  
  Purchase #6 $138.96   5.279%   $146.2957   $146.30   $146.30   $146.30  
  Purchase #7 $219.96   5.801%   $232.7199   $232.72   $232.70   $232.70  
  7 purchase totals = $953.82       $1,043.9420   $1,043.94   $1,043.90   $1,043.90