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 $108.66   11.832%   $121.5167   $121.52   $121.50   $121.50  
  Purchase #2 $164.40   10.270%   $181.2839   $181.28   $181.30   $181.30  
  Purchase #3 $212.84   8.510%   $230.9527   $230.95   $230.95   $231.00  
  Purchase #4 $199.69   11.464%   $222.5825   $222.58   $222.60   $222.60  
  Purchase #5 $228.71   7.483%   $245.8244   $245.82   $245.80   $245.80  
  Purchase #6 $126.65   11.548%   $141.2755   $141.28   $141.30   $141.30  
  Purchase #7 $24.27   4.123%   $25.2707   $25.27   $25.25   $25.30  
  7 purchase totals = $1,065.22       $1,168.7064   $1,168.70   $1,168.70   $1,168.80