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 $34.85   4.639%   $36.4667   $36.47   $36.45   $36.50  
  Purchase #2 $237.55   13.242%   $269.0064   $269.01   $269.00   $269.00  
  Purchase #3 $94.70   8.148%   $102.4162   $102.42   $102.40   $102.40  
  Purchase #4 $230.56   3.842%   $239.4181   $239.42   $239.40   $239.40  
  Purchase #5 $149.52   13.122%   $169.14   $169.14   $169.15   $169.10  
  Purchase #6 $66.78   4.213%   $69.5934   $69.59   $69.60   $69.60  
  Purchase #7 $67.26   10.754%   $74.4931   $74.49   $74.50   $74.50  
  7 purchase totals = $881.22       $960.5339   $960.54   $960.50   $960.50