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 $243.43   13.522%   $276.3466   $276.35   $276.35   $276.30  
  Purchase #2 $200.74   4.789%   $210.3534   $210.35   $210.35   $210.40  
  Purchase #3 $121.74   5.632%   $128.5964   $128.60   $128.60   $128.60  
  Purchase #4 $43.70   3.423%   $45.1959   $45.20   $45.20   $45.20  
  Purchase #5 $106.86   5.838%   $113.0985   $113.10   $113.10   $113.10  
  Purchase #6 $10.73   9.263%   $11.7239   $11.72   $11.70   $11.70  
  Purchase #7 $45.47   6.373%   $48.3678   $48.37   $48.35   $48.40  
  7 purchase totals = $772.67       $833.6825   $833.69   $833.65   $833.70