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 $155.96   5.857%   $165.0946   $165.09   $165.10   $165.10  
  Purchase #2 $222.97   9.581%   $244.3328   $244.33   $244.35   $244.30  
  Purchase #3 $187.27   8.473%   $203.1374   $203.14   $203.15   $203.10  
  Purchase #4 $153.65   8.582%   $166.8362   $166.84   $166.85   $166.80  
  Purchase #5 $56.97   5.245%   $59.9581   $59.96   $59.95   $60.00  
  Purchase #6 $168.70   4.592%   $176.4467   $176.45   $176.45   $176.40  
  Purchase #7 $242.98   11.353%   $270.5655   $270.57   $270.55   $270.60  
  7 purchase totals = $1,188.50       $1,286.3713   $1,286.38   $1,286.40   $1,286.30