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 $61.80   9.344%   $67.5746   $67.57   $67.55   $67.60  
  Purchase #2 $128.79   11.248%   $143.2763   $143.28   $143.30   $143.30  
  Purchase #3 $24.72   4.145%   $25.7446   $25.74   $25.75   $25.70  
  Purchase #4 $153.74   13.208%   $174.046   $174.05   $174.05   $174.00  
  Purchase #5 $122.74   9.688%   $134.6311   $134.63   $134.65   $134.60  
  Purchase #6 $198.31   6.399%   $210.9999   $211.00   $211.00   $211.00  
  Purchase #7 $48.59   5.757%   $51.3873   $51.39   $51.40   $51.40  
  7 purchase totals = $738.69       $807.6598   $807.66   $807.70   $807.60