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 $222.34   11.465%   $247.8313   $247.83   $247.85   $247.80  
  Purchase #2 $188.80   3.666%   $195.7214   $195.72   $195.70   $195.70  
  Purchase #3 $244.80   12.523%   $275.4563   $275.46   $275.45   $275.50  
  Purchase #4 $60.48   4.363%   $63.1187   $63.12   $63.10   $63.10  
  Purchase #5 $87.52   4.764%   $91.6895   $91.69   $91.70   $91.70  
  Purchase #6 $175.69   10.490%   $194.1199   $194.12   $194.10   $194.10  
  Purchase #7 $171.46   13.492%   $194.5934   $194.59   $194.60   $194.60  
  7 purchase totals = $1,151.09       $1,262.5305   $1,262.53   $1,262.50   $1,262.50