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 $177.29   13.643%   $201.4777   $201.48   $201.50   $201.50  
  Purchase #2 $105.52   13.380%   $119.6386   $119.64   $119.65   $119.60  
  Purchase #3 $109.27   11.137%   $121.4394   $121.44   $121.45   $121.40  
  Purchase #4 $115.37   9.703%   $126.5644   $126.56   $126.55   $126.60  
  Purchase #5 $69.96   12.341%   $78.5938   $78.59   $78.60   $78.60  
  Purchase #6 $227.97   13.277%   $258.2376   $258.24   $258.25   $258.20  
  Purchase #7 $199.51   5.565%   $210.6127   $210.61   $210.60   $210.60  
  7 purchase totals = $1,004.89       $1,116.5642   $1,116.56   $1,116.60   $1,116.50