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 $65.53   5.212%   $68.9454   $68.95   $68.95   $68.90  
  Purchase #2 $40.75   7.362%   $43.75   $43.75   $43.75   $43.80  
  Purchase #3 $28.35   5.842%   $30.0062   $30.01   $30.00   $30.00  
  Purchase #4 $46.65   6.274%   $49.5768   $49.58   $49.60   $49.60  
  Purchase #5 $245.52   5.714%   $259.549   $259.55   $259.55   $259.50  
  Purchase #6 $179.27   4.294%   $186.9679   $186.97   $186.95   $187.00  
  Purchase #7 $119.29   9.453%   $130.5665   $130.57   $130.55   $130.60  
  7 purchase totals = $725.36       $769.3618   $769.38   $769.35   $769.40