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 $58.91   8.824%   $64.1082   $64.11   $64.10   $64.10  
  Purchase #2 $219.36   8.390%   $237.7643   $237.76   $237.75   $237.80  
  Purchase #3 $189.51   12.246%   $212.7174   $212.72   $212.70   $212.70  
  Purchase #4 $248.99   4.690%   $260.6676   $260.67   $260.65   $260.70  
  Purchase #5 $75.75   11.859%   $84.7332   $84.73   $84.75   $84.70  
  Purchase #6 $70.52   9.833%   $77.4542   $77.45   $77.45   $77.50  
  Purchase #7 $128.88   8.156%   $139.3915   $139.39   $139.40   $139.40  
  7 purchase totals = $991.92       $1,076.8364   $1,076.83   $1,076.80   $1,076.90