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 $195.55   8.506%   $212.1835   $212.18   $212.20   $212.20  
  Purchase #2 $131.51   10.826%   $145.7473   $145.75   $145.75   $145.70  
  Purchase #3 $226.64   12.113%   $254.0929   $254.09   $254.10   $254.10  
  Purchase #4 $195.87   13.113%   $221.5544   $221.55   $221.55   $221.60  
  Purchase #5 $47.99   9.442%   $52.5212   $52.52   $52.50   $52.50  
  Purchase #6 $55.39   12.732%   $62.4423   $62.44   $62.45   $62.40  
  Purchase #7 $222.52   10.311%   $245.464   $245.46   $245.45   $245.50  
  7 purchase totals = $1,075.47       $1,194.0056   $1,193.99   $1,194.00   $1,194.00