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 $139.66   8.205%   $151.1191   $151.12   $151.10   $151.10  
  Purchase #2 $224.86   12.270%   $252.4503   $252.45   $252.45   $252.50  
  Purchase #3 $157.78   13.185%   $178.5833   $178.58   $178.60   $178.60  
  Purchase #4 $213.92   5.460%   $225.6   $225.60   $225.60   $225.60  
  Purchase #5 $129.54   4.653%   $135.5675   $135.57   $135.55   $135.60  
  Purchase #6 $196.29   13.627%   $223.0384   $223.04   $223.05   $223.00  
  Purchase #7 $26.93   12.766%   $30.3679   $30.37   $30.35   $30.40  
  7 purchase totals = $1,088.98       $1,196.7265   $1,196.73   $1,196.70   $1,196.80