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 $241.65   9.247%   $263.9954   $264.00   $264.00   $264.00  
  Purchase #2 $98.78   7.398%   $106.0877   $106.09   $106.10   $106.10  
  Purchase #3 $128.37   7.458%   $137.9438   $137.94   $137.95   $137.90  
  Purchase #4 $93.62   3.742%   $97.1233   $97.12   $97.10   $97.10  
  Purchase #5 $247.35   11.489%   $275.768   $275.77   $275.75   $275.80  
  Purchase #6 $230.77   5.473%   $243.4   $243.40   $243.40   $243.40  
  Purchase #7 $138.41   10.684%   $153.1977   $153.20   $153.20   $153.20  
  7 purchase totals = $1,178.95       $1,277.5159   $1,277.52   $1,277.50   $1,277.50