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 $85.73   10.270%   $94.5345   $94.53   $94.55   $94.50  
  Purchase #2 $130.33   4.641%   $136.3786   $136.38   $136.40   $136.40  
  Purchase #3 $189.65   13.723%   $215.6757   $215.68   $215.70   $215.70  
  Purchase #4 $240.68   9.172%   $262.7552   $262.76   $262.75   $262.80  
  Purchase #5 $140.78   10.506%   $155.5703   $155.57   $155.55   $155.60  
  Purchase #6 $191.50   5.473%   $201.9808   $201.98   $202.00   $202.00  
  Purchase #7 $188.32   4.220%   $196.2671   $196.27   $196.25   $196.30  
  7 purchase totals = $1,166.99       $1,263.1622   $1,263.17   $1,263.20   $1,263.30