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 $61.97   13.369%   $70.2548   $70.25   $70.25   $70.30  
  Purchase #2 $234.95   13.305%   $266.2101   $266.21   $266.20   $266.20  
  Purchase #3 $225.68   4.763%   $236.4291   $236.43   $236.45   $236.40  
  Purchase #4 $121.76   12.593%   $137.0932   $137.09   $137.10   $137.10  
  Purchase #5 $96.72   6.132%   $102.6509   $102.65   $102.65   $102.70  
  Purchase #6 $200.46   3.173%   $206.8206   $206.82   $206.80   $206.80  
  Purchase #7 $225.96   4.424%   $235.9565   $235.96   $235.95   $236.00  
  7 purchase totals = $1,167.50       $1,255.4152   $1,255.41   $1,255.40   $1,255.50