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 $64.55   6.309%   $68.6225   $68.62   $68.60   $68.60  
  Purchase #2 $237.73   5.445%   $250.6744   $250.67   $250.65   $250.70  
  Purchase #3 $14.76   7.375%   $15.8486   $15.85   $15.85   $15.80  
  Purchase #4 $32.71   9.579%   $35.8433   $35.84   $35.85   $35.80  
  Purchase #5 $218.81   11.524%   $244.0257   $244.03   $244.05   $244.00  
  Purchase #6 $243.27   10.569%   $268.9812   $268.98   $269.00   $269.00  
  Purchase #7 $40.27   3.705%   $41.762   $41.76   $41.75   $41.80  
  7 purchase totals = $852.10       $925.7577   $925.75   $925.75   $925.70