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 $53.26   6.470%   $56.7059   $56.71   $56.70   $56.70  
  Purchase #2 $159.81   13.441%   $181.2901   $181.29   $181.30   $181.30  
  Purchase #3 $196.31   11.735%   $219.347   $219.35   $219.35   $219.30  
  Purchase #4 $55.91   13.229%   $63.3063   $63.31   $63.30   $63.30  
  Purchase #5 $8.40   7.644%   $9.0421   $9.04   $9.05   $9.00  
  Purchase #6 $218.30   12.114%   $244.7449   $244.74   $244.75   $244.70  
  Purchase #7 $173.76   4.446%   $181.4854   $181.49   $181.50   $181.50  
  7 purchase totals = $865.75       $955.9217   $955.93   $955.95   $955.80