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 $160.35   4.344%   $167.3156   $167.32   $167.30   $167.30  
  Purchase #2 $177.97   7.579%   $191.4583   $191.46   $191.45   $191.50  
  Purchase #3 $226.76   4.522%   $237.0141   $237.01   $237.00   $237.00  
  Purchase #4 $132.94   6.531%   $141.6223   $141.62   $141.60   $141.60  
  Purchase #5 $246.59   11.350%   $274.578   $274.58   $274.60   $274.60  
  Purchase #6 $192.84   4.434%   $201.3905   $201.39   $201.40   $201.40  
  Purchase #7 $51.98   8.778%   $56.5428   $56.54   $56.55   $56.50  
  7 purchase totals = $1,189.43       $1,269.9216   $1,269.92   $1,269.90   $1,269.90