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 $130.48   8.802%   $141.9648   $141.96   $141.95   $142.00  
  Purchase #2 $105.61   4.446%   $110.3054   $110.31   $110.30   $110.30  
  Purchase #3 $27.36   12.138%   $30.681   $30.68   $30.70   $30.70  
  Purchase #4 $177.73   11.211%   $197.6553   $197.66   $197.65   $197.70  
  Purchase #5 $183.59   8.155%   $198.5618   $198.56   $198.55   $198.60  
  Purchase #6 $67.83   11.510%   $75.6372   $75.64   $75.65   $75.60  
  Purchase #7 $177.41   8.515%   $192.5165   $192.52   $192.50   $192.50  
  7 purchase totals = $870.01       $947.3220   $947.33   $947.30   $947.40