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 $49.57   8.731%   $53.898   $53.90   $53.90   $53.90  
  Purchase #2 $31.83   5.604%   $33.6138   $33.61   $33.60   $33.60  
  Purchase #3 $73.86   8.663%   $80.2585   $80.26   $80.25   $80.30  
  Purchase #4 $35.32   11.450%   $39.3641   $39.36   $39.35   $39.40  
  Purchase #5 $166.61   9.226%   $181.9814   $181.98   $182.00   $182.00  
  Purchase #6 $198.58   3.844%   $206.2134   $206.21   $206.20   $206.20  
  Purchase #7 $180.53   13.754%   $205.3601   $205.36   $205.35   $205.40  
  7 purchase totals = $736.30       $800.6893   $800.68   $800.65   $800.80