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 $64.42   8.433%   $69.8525   $69.85   $69.85   $69.90  
  Purchase #2 $139.70   13.568%   $158.6545   $158.65   $158.65   $158.70  
  Purchase #3 $141.31   7.570%   $152.0072   $152.01   $152.00   $152.00  
  Purchase #4 $237.72   13.206%   $269.1133   $269.11   $269.10   $269.10  
  Purchase #5 $111.70   9.817%   $122.6656   $122.67   $122.65   $122.70  
  Purchase #6 $134.70   4.530%   $140.8019   $140.80   $140.80   $140.80  
  Purchase #7 $93.60   11.649%   $104.5035   $104.50   $104.50   $104.50  
  7 purchase totals = $923.15       $1,017.5985   $1,017.59   $1,017.55   $1,017.70