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 $106.43   11.491%   $118.6599   $118.66   $118.65   $118.70  
  Purchase #2 $34.98   8.520%   $37.9603   $37.96   $37.95   $38.00  
  Purchase #3 $87.42   8.695%   $95.0212   $95.02   $95.00   $95.00  
  Purchase #4 $197.99   8.335%   $214.4925   $214.49   $214.50   $214.50  
  Purchase #5 $126.93   3.211%   $131.0057   $131.01   $131.00   $131.00  
  Purchase #6 $49.76   9.339%   $54.4071   $54.41   $54.40   $54.40  
  Purchase #7 $214.78   13.442%   $243.6507   $243.65   $243.65   $243.70  
  7 purchase totals = $818.29       $895.1974   $895.20   $895.15   $895.30