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 $169.61   8.558%   $184.1252   $184.13   $184.15   $184.10  
  Purchase #2 $108.34   7.681%   $116.6616   $116.66   $116.65   $116.70  
  Purchase #3 $41.76   9.398%   $45.6846   $45.68   $45.70   $45.70  
  Purchase #4 $38.33   13.554%   $43.5252   $43.53   $43.55   $43.50  
  Purchase #5 $215.30   8.854%   $234.3627   $234.36   $234.35   $234.40  
  Purchase #6 $24.52   8.231%   $26.5382   $26.54   $26.55   $26.50  
  Purchase #7 $121.34   8.289%   $131.3979   $131.40   $131.40   $131.40  
  7 purchase totals = $719.20       $782.2954   $782.30   $782.35   $782.30