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 $205.64   7.610%   $221.2892   $221.29   $221.30   $221.30  
  Purchase #2 $93.45   6.719%   $99.7289   $99.73   $99.75   $99.70  
  Purchase #3 $70.68   3.372%   $73.0633   $73.06   $73.05   $73.10  
  Purchase #4 $68.52   10.307%   $75.5824   $75.58   $75.60   $75.60  
  Purchase #5 $167.36   10.458%   $184.8625   $184.86   $184.85   $184.90  
  Purchase #6 $35.41   11.260%   $39.3972   $39.40   $39.40   $39.40  
  Purchase #7 $53.73   9.830%   $59.0117   $59.01   $59.00   $59.00  
  7 purchase totals = $694.79       $752.9352   $752.93   $752.95   $753.00