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 $59.72   12.573%   $67.2286   $67.23   $67.25   $67.20  
  Purchase #2 $15.36   12.435%   $17.27   $17.27   $17.25   $17.30  
  Purchase #3 $214.92   13.336%   $243.5817   $243.58   $243.60   $243.60  
  Purchase #4 $235.76   4.138%   $245.5157   $245.52   $245.50   $245.50  
  Purchase #5 $67.76   11.759%   $75.7279   $75.73   $75.75   $75.70  
  Purchase #6 $49.44   6.104%   $52.4578   $52.46   $52.45   $52.50  
  Purchase #7 $230.52   5.162%   $242.4194   $242.42   $242.40   $242.40  
  7 purchase totals = $873.48       $944.2011   $944.21   $944.20   $944.20