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 $127.76   5.673%   $135.0078   $135.01   $135.00   $135.00  
  Purchase #2 $158.25   5.227%   $166.5217   $166.52   $166.50   $166.50  
  Purchase #3 $164.37   5.486%   $173.3873   $173.39   $173.40   $173.40  
  Purchase #4 $217.36   6.489%   $231.4645   $231.46   $231.45   $231.50  
  Purchase #5 $22.59   9.418%   $24.7175   $24.72   $24.70   $24.70  
  Purchase #6 $172.94   5.490%   $182.4344   $182.43   $182.45   $182.40  
  Purchase #7 $45.48   6.469%   $48.4221   $48.42   $48.40   $48.40  
  7 purchase totals = $908.75       $961.9553   $961.95   $961.90   $961.90