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 $181.39   8.801%   $197.3541   $197.35   $197.35   $197.40  
  Purchase #2 $122.81   11.377%   $136.7821   $136.78   $136.80   $136.80  
  Purchase #3 $20.80   8.361%   $22.5391   $22.54   $22.55   $22.50  
  Purchase #4 $233.47   13.205%   $264.2997   $264.30   $264.30   $264.30  
  Purchase #5 $168.49   10.844%   $186.7611   $186.76   $186.75   $186.80  
  Purchase #6 $123.84   6.352%   $131.7063   $131.71   $131.70   $131.70  
  Purchase #7 $102.99   8.809%   $112.0624   $112.06   $112.05   $112.10  
  7 purchase totals = $953.79       $1,051.5048   $1,051.50   $1,051.50   $1,051.60