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 $248.89   6.707%   $265.5831   $265.58   $265.60   $265.60  
  Purchase #2 $152.58   11.266%   $169.7697   $169.77   $169.75   $169.80  
  Purchase #3 $180.50   11.292%   $200.8821   $200.88   $200.90   $200.90  
  Purchase #4 $105.52   9.352%   $115.3882   $115.39   $115.40   $115.40  
  Purchase #5 $17.36   10.720%   $19.221   $19.22   $19.20   $19.20  
  Purchase #6 $44.53   12.235%   $49.9782   $49.98   $50.00   $50.00  
  Purchase #7 $225.34   3.191%   $232.5306   $232.53   $232.55   $232.50  
  7 purchase totals = $974.72       $1,053.3529   $1,053.35   $1,053.40   $1,053.40