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 $97.78   12.455%   $109.9585   $109.96   $109.95   $110.00  
  Purchase #2 $45.73   6.147%   $48.541   $48.54   $48.55   $48.50  
  Purchase #3 $59.80   3.682%   $62.0018   $62.00   $62.00   $62.00  
  Purchase #4 $111.57   6.811%   $119.169   $119.17   $119.15   $119.20  
  Purchase #5 $111.30   8.154%   $120.3754   $120.38   $120.40   $120.40  
  Purchase #6 $229.97   9.778%   $252.4565   $252.46   $252.45   $252.50  
  Purchase #7 $49.53   6.458%   $52.7286   $52.73   $52.75   $52.70  
  7 purchase totals = $705.68       $765.2308   $765.24   $765.25   $765.30